Potential emerging therapeutic strategies to prevent restenosis in the peripheral vasculature

Platelet Aggregability as a Predictor of Restenosis Following Carotid Endarterectomy

BACKGROUND

Antiplatelet drugs are administered before and after carotid endarterectomies (CEAs), but their efficacy for preventing restenosis remains unclear. Hence, this study aimed to identify associations between postoperative restenosis and platelet aggregability in CEA patients.

METHODS

Thirty-six consecutive CEA patients treated at Tokyo Women's Medical University from May 2013 to March 2015 were included in this retrospective study. Restenosis was defined as a stenosis ratio greater than or equal to 50% per the European Carotid Surgery Trial criteria or peak systolic velocity of 150 cm/s on carotid ultrasound. Platelet aggregability was measured turbidimetrically using a light-transmission platelet aggregometer and analyzed in terms of aggregation profiles for 2 concentrations of collagen used to induce aggregation (.25 and 2.0 μg/mL). Patients were automatically divided into 9 classes (Class 1-9, from the lowest to the highest aggregability) using a software program according to area under their platelet aggregation curves. Each class was subdivided into 10 further gradations for a total of 90 possible scores (10-99) using a software program. Patients were divided into high- and low-platelet aggregability score groups (cut-off = 49).

RESULTS

Data were analyzed for 36 of the 99 patients. Restenosis was observed in 10 (28%) patients. Restenosis incidence was significantly higher in patients with high-platelet aggregability score than in those with low-platelet aggregability score (50.0% [7/14] versus 13.6% [3 of 22]: P = .0176, odds ratio = 6.34, 95% CI: 1.27-31.57).

CONCLUSIONS

Platelet aggregability is a useful metric for predicting and preventing restenosis after CEA. It has potential as an indicator for determining the optimal dose of antiplatelet drugs.

Drug- and Gene-eluting Stents for Preventing Coronary Restenosis

Coronary artery disease (CAD) has been reported to be a major cause of death worldwide. Current treatment methods include atherectomy, coronary angioplasty (as a percutaneous coronary intervention), and coronary artery bypass. Among them, the insertion of stents into the coronary artery is one of the commonly used methods for CAD, although the formation of in-stent restenosis (ISR) is a major drawback, demanding improvement in stent technology. Stents can be improved using the delivery of DNA, siRNA, and miRNA rather than anti-inflammatory/anti-thrombotic drugs. In particular, genes that could interfere with the development of plaque around infected regions are conjugated on the stent surface to inhibit neointimal formation. Despite their potential benefits, it is necessary to explore the various properties of gene-eluting stents. Furthermore, multifunctional electronic stents that can be used as a biosensor and deliver drug- or gene-based on physiological condition will be a very promising way to the successful treatment of ISR. In this review, we have discussed the molecular mechanism of restenosis, the use of drug- and gene-eluting stents, and the possible roles that these stents have in the prevention and treatment of coronary restenosis. Further, we have explained how multifunctional electronic stents could be used as a biosensor and deliver drugs based on physiological conditions.

A Review of the Principles and Use of Lasers in Lower Limb Problems

Lasers present a unique light source with many clinical uses including a number of applications relevant to the lower extremity. In this article, the basic principles of lasers and their interactions with tissue will be reviewed. The article examines laser applications in skin and vascular disease including wound healing. The principles of laser safety are discussed, and relevant future developments are considered.

Role of biomaterials in prevention of in-stent restenosis

Coronary balloon angioplasty and coronary stenting are the procedures used in healing coronary artery disease. However, injury of arteries during angioplasty and stenting causes cell stimulations in tissue. Cell movement and thrombosis lead to re-narrowing of widened vessel called restenosis. Several new types of carriers and technology have been developed to suppress and/or prevent restenosis. Authors review the polymeric materials featured in drug/gene carrier systems, nanovehicles, and stent coating materials against restenosis.

Drug packaging and delivery using perfluorocarbon nanoparticles for targeted inhibition of vascular smooth muscle cells

AIM

To investigate the in vitro release profile of drugs encapsulated within perfluorocarbon (PFC) nanoparticles (NPs) and their ability to inhibit the activity of vascular smooth muscle cells (SMCs).

METHODS

Dexamethasone phosphate (DxP) or dexamethasone acetate (DxA) was encapsulated into PFC nanoparticles using a high-pressure homogenous method. The morphology and size of the NPs were examined using scanning electron microscopy (SEM) and a laser particle size analyzer. Drug loading and in vitro release were assessed by high-performance liquid chromatography (HPLC). The impact of NP capsules on SMC proliferation, migration and apoptosis in vitro was assessed using cell counting kit-8, transwell cell migration and flow cytometry assays.

RESULTS

The sizes of DxP-NPs and DxA-NPs were 224+/-6 nm and 236+/-9 nm, respectively. The encapsulation efficiency (EE) of DxP-NPs was 66.4%+/-1.0%, with an initial release rate of 77.2%, whereas the EE of DxA-NPs was 95.3%+/-1.3%, with an initial release rate of 23.6%. Both of the NP-coated drugs could be released over 7 d. Human umbilical artery SMCs were harvested and cultured for four to six passages. Compared to free DxP, SMCs treated with tissue factor (TF)-directed DxP-NPs showed significant differences in the inhibition of proliferation, migration and apoptosis (P<0.05).

CONCLUSION

The results collectively suggest that PFC nanoparticles will be beneficial for targeted drug delivery because of the sustained drug release and effective inhibition of SMC proliferation and migration.

The tissue plasminogen activator gene promoter: a novel tool for radiogenic gene therapy of the prostate?

BACKGROUND

Radiation therapy is a treatment modality routinely used in cancer management so it is not unexpected that radiation-inducible promoters have emerged as an attractive tool for controlled gene therapy. The human tissue plasminogen activator gene promoter (t-PA) has been proposed as a candidate for radiogenic gene therapy, but has not been exploited to date. The purpose of this study was to evaluate the potential of this promoter to drive the expression of a reporter gene, the green fluorescent protein (GFP), in response to radiation exposure.

METHODS

To investigate whether the promoter could be used for prostate cancer gene therapy, we initially transfected normal and malignant prostate cells. We then transfected HMEC-1 endothelial cells and ex vivo rat tail artery and monitored GFP levels using Western blotting following the delivery of single doses of ionizing radiation (2, 4, 6 Gy) to test whether the promoter could be used for vascular targeted gene therapy.

RESULTS

The t-PA promoter induced GFP expression up to 6-fold in all cell types tested in response to radiation doses within the clinical range.

CONCLUSIONS

These results suggest that the t-PA promoter may be incorporated into gene therapy strategies driving therapeutic transgenes in conjunction with radiation therapy.

Successful revascularization of re-stenosis of lower extremity arteries with localized delivery of paclitaxel

Restenosis after percutaneous revascularization techniques is a challenging issue in patients with severe peripheral arterial disease. We report two cases where multiple revascularization techniques had been used previously, but restenosis occurred. We used an irrigation balloon to deliver paclitaxel locally into the tissues to obtain better results.

Delivery of large biopharmaceuticals from cardiovascular stents: a review

This review focuses on new and emerging large-molecule bioactive agents delivered from stent surfaces in drug-eluting stents (DESs) to inhibit vascular restenosis in the context of interventional cardiology. New therapeutic agents representing proteins, nucleic acids (small interfering RNAs and large DNA plasmids), viral delivery vectors, and even engineered cell therapies require specific delivery designs distinct from traditional smaller-molecule approaches on DESs. While small molecules are currently the clinical standard for coronary stenting, extension of the DESs to other lesion types, peripheral vasculature, and nonvasculature therapies will seek to deliver an increasingly sophisticated armada of drug types. This review describes many of the larger-molecule and biopharmaceutical approaches reported recently for stent-based delivery with the challenges associated with formulating and delivering these drug classes compared to the current small-molecule drugs. It also includes perspectives on possible future applications that may improve safety and efficacy and facilitate diversification of the DESs to other clinical applications.

Beta radiation in the treatment of in-stent restenosis of an in situ saphenous vein bypass graft A case report

We describe a case of instent restenosis in a femoral-distal saphenous vein bypass graft successfully treated with brachytherapy. A 45-year-old insulin-requiring diabetic woman underwent an in-situ femoral-anterior tibial bypass graft for a non-healing ischemic ulcer. Despite a technically successful percutaneous transluminal angioplasty and endovascular stenting of a retained valve within the threatened graft, the wound failed to heal. At the 1-month follow-up, instent restenosis was documented and successful cutting balloon angioplasty, complemented by adjunctive beta-irradiation was successfully performed. Clinical and hemodynamic success was achieved, with prompt ulcer healing and intermediate-term graft patency maintained on surveillance duplex ultrasound follow-up. We review the literature on radiation therapy in the management of peripheral arterial disease and discuss therapeutic options in the management of restenosis.

Endovascular Interventions in Iliac and Infrainguinal Occlusive Artery Disease

Percutaneous endovascular procedures are increasingly applied to treat symptomatic peripheral occlusive artery disease. While the primary technical success and recanalization rates in iliac and infrainguinal interventions are high, differences in the long-term patency rates exist with respect to the anatomic localization, separating the iliac, femoropopliteal, and infrapopliteal arterial regions. In iliac arteries, even complex lesions can be recanalized with good long-term patency rates, especially when using self-expanding nitinol stents. In the infrainguinal arteries the method of choice is still under debate (e.g., balloon angioplasty vs stent implantation). A high restenosis rate represents one of the major limitations in femoropopliteal and infrapopliteal interventions. Therefore, additional methods and treatment strategies for peripheral interventions with the potential for future applications are under investigation and will be discussed such as drug-eluting stents, brachytherapy, subintimal angioplasty, laser angioplasty, atherectomy/thrombectomy, cutting balloon, polytetrafluoroethylene (PTFE)-covered stent grafts, biodegradable stents, and cryoplasty. The increasing amount of data on successful peripheral interventions supports the necessity to adapt and reevaluate the current consensus guidelines that were put together in 2000.

Saratin (an inhibitor of platelet-collagen interaction) decreases platelet aggregation and homocysteine-mediated postcarotid endarterectomy intimal hyperplasia in a dose-dependent manner

BACKGROUND

This study investigated Saratin's (Merck KGaA, Darmstadt, Germany) prevention of platelet adhesion and intimal hyperplasia at different doses and in the hyperhomocystinemia rat carotid endarterectomy (CEA) model.

METHODS

Rats were divided into two groups: (1) platelet adhesion or (2) luminal stenosis because of intimal hyperplasia. At CEA, rats received 0, 0.5, 5.0, 10.0, or 20.0 microg Saratin on the artery. Post-CEA platelet aggregation was evaluated by standard error of the mean. Intimal hyperplasia group received either (1) control or (2) 4.5 g/kg DL-homocystine diets for two weeks followed by CEA and treated with diluent or 5.0 microg Saratin. Endpoints included platelet adhesion, intimal hyperplasia, plasma homocysteine (HCys), and its metabolic enzymes cystathionine beta-synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR).

RESULTS

Platelet adhesion: post-CEA, platelet adhesion was reduced by 63%, 67%, and 67% in Saratin doses > or =5.0 microg. Intimal hyperplasia: 5.0 microg Saratin in the HCys group decreased intimal hyperplasia by 45% compared with the non-Saratin-treated HCys group. Plasma HCys levels were not altered with Saratin treatment in the HCys groups nor were CBS or MTHFR.

CONCLUSIONS

Saratin significantly inhibited platelet adhesion at > or =5.0 microg, and Saratin at 5.0 microg attenuated luminal stenosis in a hyperhomocysteinemic rat CEA model.

Perivascular delivery of losartan with surgical fibrin glue prevents neointimal hyperplasia after arterial injury

OBJECTIVE

Long-term success of revascularization procedures is limited by recurrent stenosis, a reduction in vascular lumen area that results from neointimal hyperplasia. Inhibitors of the renin-angiotensin system, such as losartan, have potential to prevent recurrent stenosis; however, to date, efficacy has not been demonstrated in either animal models or human beings. While we have previously reported that treatment with a satisfactory dose may be an important element in obtaining efficacy, oral delivery cannot achieve the required concentration. We therefore tested the ability of losartan to restrict neointimal hyperplasia after local delivery of an elevated dose in a fibrin glue.

METHODS

The porcine saphenous artery was subjected to balloon angioplasty. Losartan (25 micromol/mL) was applied directly to the adventitial surface of the injured vessel after mixing with 1.0 mL of Tisseel. Neointimal formation was quantified after 14 days with morphometry, and immunologic staining was used to monitor expression of proteins associated with cell proliferation, migration, and phenotypic modulation.

RESULTS

A statistically significant decrease of 82% (n = 5) in neointimal area was obtained with losartan, and cell proliferation, as defined by proliferating cell nuclear antigen (PCNA) expression, was inhibited by 97%. Reduced cyclin A expression in losartan-treated vessels confirmed that cell cycle progression was blocked; however, the presence of cytokeratin 8 and tenascin in the media and neointima of injured vessels, regardless of treatment, suggested that losartan does not restrict phenotypic modulation. Inhibition of MT1-MMP (MMP-14) expression by losartan indicated that this inhibitor likely suppresses cell migration as well.

CONCLUSIONS

These data demonstrate that losartan can effectively prevent recurrent stenosis when delivered locally with a fibrin glue such as Tisseel. Our results also indicate that losartan may operate by interfering with the expression of proteins required for cell cycle progression and migration.

CLINICAL RELEVANCE

Release of angiotensin II in response to vascular injury may promote neointimal hyperplasia, because this hormone can stimulate smooth muscle cell proliferation and migration. This study demonstrates that local application of an angiotensin receptor antagonist, losartan, to the site of injury can effectively prevent neointimal hyperplasia after balloon angioplasty. Application of losartan to the perivascular surface of the injured vessel in a surgical fibrin glue enabled delivery of a dose that exceeds the maximum attainable, via a systemic delivery route. The glue also served as a depot from which the drug was slowly released over time. Treatment with losartan may be a viable approach for controlling neointimal hyperplasia at locations (eg, grafts) that are accessible during a surgical procedure.

Gene therapy for cardiovascular angiogenesis

Atherosclerosis and endothelial dysfunction are responsible for the pathophysiologic basis of the spectrum of cardiovascular disorders including ischaemic heart disease (IHD), the leading cause of morbidity and mortality in the US. There have been major advances, including the use of pharmacotherapy, coronary and peripheral percutaneous transluminal interventions (PTI), coronary and peripheral bypass surgery and primary/secondary prevention measures. There are, however, multiple unmet needs: IHD refractory to medical therapy and unsuitable for revascularisation; critical limb ischaemia unsuitable for PTI or surgery; restenosis; ischaemic/diabetic neuropathy and heart failure. Cardiovascular gene therapy (GT) with vascular endothelial growth factor (VEGF) has yielded improved perfusion and reduced ischaemia in preclinical models of IHD. Several preclinical studies and Phase I and II clinical trials have shown the safety and therapeutic potential of GT in the treatment of IHD, peripheral arterial disease (PAD), restenosis, and ischaemic and diabetic neuropathy, pointing to the need for Phase III clinical trials.