Treatment of in-stent restenosis with beraprost sodium: an experimental study of short- and intermediate-term effects in dogs

Histological Features of In-Stent Restenosis after Iliac Vein Thrombus Removal and Stent Placement in a Goat Model

PURPOSE

To establish an animal model for in-stent restenosis (ISR) after postthrombotic iliac vein stent placement and characterize histopathological changes in tissue within the stented vein.

MATERIALS AND METHODS

Iliac vein thrombosis was induced using balloon occlusion and thrombin injection in 8 male Boer goats. Mechanical thrombectomy and iliac vein stent placement were performed 3 days after thrombosis induction. Restenosis was evaluated by venography and optical coherence tomography (OCT) at 1 and 8 weeks after stent placement, and stent specimens were taken for pathological examination after the animals were euthanized.

RESULTS

Thrombosis induction was successful in all 8 goats, with >80% iliac vein occlusion. After thrombus removal, OCT revealed considerable venous intimal thickening and a small number of mural thrombi. Neointimal hyperplasia with thrombus formation was observed in all goats 1 week after stent implantation; the degree of ISR was 15%-33%. At 8 weeks, the degree of ISR was 21%-32% in 3 goats, and stent occlusion was observed in 1 goat. At 1 week, the neointima predominantly consisted of fresh thrombi. At 8 weeks, proliferplastic fibrotic tissue and smooth muscle cells (SMCs) were predominant, and the stent surfaces were endothelialized in 2 of 3 goats and partially endothelialized in 1 goat.

CONCLUSIONS

In the goat model, postthrombotic neointimal hyperplasia in the venous stent may result from time-dependent thrombus formation and organization, accompanied by migration and proliferation of SMCs, causing ISR. These results provide a basis to further explore the mechanism of venous ISR and promote the development of venous stents that reduce neointimal hyperplasia.

Drug-coated balloon therapy for in-stent restenosis in patients with iliofemoral deep vein thrombosis: A single-arm observational study

BACKGROUND

Iliofemoral deep vein thrombosis (IFDVT) causes severe symptoms and affect the quality of life to a great extent. Endovascular thrombectomy and stent implantation have been a feasible strategie to alleviate the signs and symptoms of IFDVT. However, venous in-stent restenosis (ISR) has become an emerging non-negligible problem.

METHODS

To evaluate the histological characteristics of venous ISR, neointima of arterial and venous ISR patients were collected and examed. To explore the effect of drug-coated balloon (DCB) on venous ISR lesions, we conducted a single-center retrospective case series study involving IFDVT patients with ISR after venous stenting who were treated with paclitaxel-coated balloon dilatation.

RESULTS

We found a collagen-rich matrix but not elastin, as well as fewer cells and less neovascularization in venous intimal hyperplasia compared with neointima in arteries. Thirteen IFDVT patients were involved in the study, with average preoperative stenosis degree of 87.69% ± 13.48%. After intervention, the stenosis degree was significantly reduced to 14.6% ± 14.36% immediately (p < 0.0001) and to 16.54% ± 15.73% during follow-up (p < 0.0001). During follow-up, the VEINES-QOL scores (p < 0.0001), VEINES-Sym scores (p < 0.0001), and Villalta scores (p = 0.04) of patients was improved significantly compared with those before intervention. No major adverse events were observed.

CONCLUSIONS

The use of DCB may have a positive effect in the treatment of venous ISR by targeting intimal hyperplasia. Moreover, the application of DCB dilatation in IFDVT stenting patients with ISR is deemed safe and effective.

Angioscopic evaluation after venous stents

BACKGROUND

Venous stenting is increasingly used to manage femoro-ilio-caval venous outflow obstruction/stenosis due to post-thrombotic syndrome. Although the safety, efficacy, and long-term patency of venous stents have been reported, re-interventions due to stent occlusion and in-stent restenosis (ISR) have also been reported. The mechanism of ISR and the in-stent neointimal growth after venous stenting remains unclear. We performed angioscopy to evaluate intraluminal details after venous stenting, allowing real-time direct visualization of the vessel lumen.

METHODS

Ten angioscopic procedures in four patients with post-thrombotic syndrome were performed. All evaluated vessels were stented iliac veins, and their native pathology was chronic post-thrombotic occlusion. Nine procedures in three patients underwent serial evaluation of the neointimal changes after stent implantation to study the natural time course of neointimal proliferation/coverage over the stent. The serial follow-up angioscopic evaluations were performed at the end of the venous stent deployment procedure, and at 6 months, 12 months, and 24 months. One procedure was performed 1 month after the stent implantation to evaluate ISR, which was observed at the first month of routine stent surveillance. A 5.7F angioscope was used to visualize the target veins. Continuous irrigation was used to displace blood and clear the visual field.

RESULTS

At 6 months after stent implantation, stent struts were covered by a thin neointima in two of the three patients. The struts were partially covered in one patient, but there was little neointimal growth overall. Neointimal coverage increased over time, and at 12 months stent struts in 2 patients were almost completely covered. There was no significant change between the 12 and 24 months after stent implantation. In the ISR case, angioscopy demonstrated an overgrown thickened neointima, and the stent struts were fully embedded and invisible in the entire stented area. No thrombus and no webs or trabeculae were found in the area evaluated as an ISR lesion.

CONCLUSIONS

At 6 months after stent placement, the stent struts were almost covered by a neointima. The stent struts were completely covered 1 year after stent implantation. Neointimal coverage was unchanged from the 1-year follow-up to the 2-year follow-up, suggesting that neointimal proliferation proceeded gradually with subsequent neointimal remodeling up to 1 year. The cause of ISR might be the overgrown thickened neointima rather than the formation of thrombosis.

An overview of in-stent restenosis in iliofemoral venous stents

BACKGROUND

Although endovenous stents have been associated with overall low morbidity, they can require reinterventions to correct stent malfunction due to in-stent restenosis (ISR). ISR has often occurred iliofemoral venous stents but has not been well described. It has been reported to develop in >70% of patients who have undergone iliofemoral venous stenting. We sought to provide an overview of ISR in iliofemoral venous stents, including the pathologic, diagnostic, and management considerations and the identification of several areas of potential research in the future.

METHODS

A search of reported English-language studies was performed in PubMed and the Cochrane Library. "In-stent restenosis," "vein," "venous," "iliac," and "iliofemoral" were used as keywords. The pertinent reports included in the present review had addressed the pathology, diagnosis, and current management options for ISR.

RESULTS

ISR refers to the narrowing of the luminal caliber of the stent owing to the development of stenosis inside the stent itself. ISR should be differentiated from stent compression. Two main types of ISR have been described: soft and hard lesions. These lesions respond differently to angioplasty. Stent inflow and shear stress are important factors in the development of ISR. The treatment options available at present include balloon angioplasty (hyperdilation or isodilation), laser ablation, atherectomy, and Z-stent placement.

CONCLUSIONS

Reintervention for ISR should be determined by the presence of residual or recurrent symptoms and not simply by a numeric value obtained from an imaging study. Overall stent occlusion due to ISR is rare, and no role exists for prophylactic angioplasty to treat asymptomatic ISR. The current treatment options for ISR are mostly durable and effective. However, more research is needed on methods to prevent the development of ISR. The role of antiplatelet and anticoagulant agents in the prevention of ISR requires further investigation, with particular attention to unique subset of patients (after thrombosis vs nonthrombotic iliac vein lesions). For high-risk, post-thrombotic patients, anticoagulation can be considered to prevent ISR. The role of triple therapy (anticoagulation and dual antiplatelet therapy) in the prevention of ISR remains unclear.

Altered expression of eNOS, prostacyclin synthase, prostaglandin G/H synthase, and thromboxane synthase in porcine aortic endothelial cells after exposure to human serum-relevance to xenotransplantation

Under normal conditions, the activity of platelets is stringently and precisely balanced between activation and quiescent state. This guarantees rapid hemostasis and avoids uncontrolled thrombosis. However, excessive platelet activation and resulting thrombotic microangiopathy are frequently observed in pig-to-primate xenotransplantation models. Endothelium-derived inhibitory mechanisms play an important role in regulation of platelet activation. These mainly include nitric oxide (NO), prostacyclin PGI₂ , and adenosine, which are synthesized by endothelial NO synthases (eNOS), prostacyclin synthase, and CD39/CD73, respectively. We investigated whether endothelium-derived regulatory mechanisms are affected in porcine aortic endothelial cells (PAECs) after exposure to human serum. In the present study, exposure of PAECs or porcine iliac arteries to human serum suppressed gene expression of eNOS and prostacyclin synthase, while induced gene expression of prostaglandin G/H synthase and thromboxane synthase. Simultaneously, exposure to human serum reduced NO and PGI₂ production in PAEC culture supernatants. Thus, human serum altered the balance of endothelium-derived inhibitory mechanisms in PAECs, which may indicate a regulatory mechanism of excessive platelet activation in pig-to-primate xenotransplantation.

The cAMP-producing agonist beraprost inhibits human vascular smooth muscle cell migration via exchange protein directly activated by cAMP

Aims

During restenosis, vascular smooth muscle cells (VSMCs) migrate from the vascular media to the developing neointima. Preventing VSMC migration is therefore a therapeutic target for restenosis. Drugs, such as prostacyclin analogues, that increase the intracellular concentration of cyclic adenosine monophosphate (cAMP) can inhibit VSMC migration, but the mechanisms via which this occurs are unknown. Two main downstream mediators of cAMP are protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). This study has examined the effects of the prostacyclin analogue beraprost on VSMC migration and investigated the intracellular pathways involved.

Methods and results

In a chemotaxis chamber, human saphenous vein VSMC migrated towards a platelet-derived growth-factor-BB (PDGF) chemogradient. Incubation with therapeutically relevant concentrations of cAMP-producing agonist beraprost significantly decreased PDGF-induced migration. Direct activation of either PKA or Epac inhibited migration whereas inhibition of PKA did not prevent the anti-migratory effect of beraprost. Direct activation of Epac also prevented hyperplasia in ex vivo serum-treated human veins. Using fluorescence resonance energy transfer, we demonstrated that beraprost activated Epac but not PKA. The mechanisms of this Epac-mediated effect involved activation of Rap1 with subsequent inhibition of RhoA. Cytoskeletal rearrangement at the leading edge of the cell was consequently inhibited. Interestingly, Epac1 was localized to the leading edge of migrating VSMC.

Conclusions

These results indicate that therapeutically relevant concentrations of beraprost can inhibit VSMC migration via a previously unknown mechanism involving the cAMP mediator Epac. This may provide a novel target that could blunt neointimal formation.

Indications for platelet aggregation inhibitors after venous stents

Iliofemoral venous obstruction may arise from either primary compressive lesions or may be secondary to an episode of deep venous thrombosis. Regardless of aetiology, these lesions, either alone or in association with more distal reflux, may be responsible for lower extremity pain, swelling, and ulceration. Conventional surgical procedures for the treatment of iliofemoral venous obstruction have largely been supplanted by endovascular approaches relying on the deployment of venous stents. Large series have reported good technical and clinical results from venous stenting, particularly for primary lesions. However, early stent occlusions and late re-stenosis do occur. Although most of these appear related to technical factors, there is likely a role for pharmacological adjuncts in maintaining stent patency. The use of anticoagulants and antiplatelet agents is largely based on the underlying pathophysiology and extrapolation from arterial interventions, which likely are significantly different with respect to their pathophysiology and natural history. Although lacking substantial evidence demonstrating efficacy, the use of adjunctive antiplatelet agents in stents placed for primary lesions and consideration of anticoagulation for high-risk post-thrombotic lesions appears to be reasonable.

Molecular mechanisms regulating the vascular prostacyclin pathways and their adaptation during pregnancy and in the newborn

Prostacyclin (PGI(2)) is a member of the prostanoid group of eicosanoids that regulate homeostasis, hemostasis, smooth muscle function and inflammation. Prostanoids are derived from arachidonic acid by the sequential actions of phospholipase A(2), cyclooxygenase (COX), and specific prostaglandin (PG) synthases. There are two major COX enzymes, COX1 and COX2, that differ in structure, tissue distribution, subcellular localization, and function. COX1 is largely constitutively expressed, whereas COX2 is induced at sites of inflammation and vascular injury. PGI(2) is produced by endothelial cells and influences many cardiovascular processes. PGI(2) acts mainly on the prostacyclin (IP) receptor, but because of receptor homology, PGI(2) analogs such as iloprost may act on other prostanoid receptors with variable affinities. PGI(2)/IP interaction stimulates G protein-coupled increase in cAMP and protein kinase A, resulting in decreased [Ca(2+)](i), and could also cause inhibition of Rho kinase, leading to vascular smooth muscle relaxation. In addition, PGI(2) intracrine signaling may target nuclear peroxisome proliferator-activated receptors and regulate gene transcription. PGI(2) counteracts the vasoconstrictor and platelet aggregation effects of thromboxane A(2) (TXA(2)), and both prostanoids create an important balance in cardiovascular homeostasis. The PGI(2)/TXA(2) balance is particularly critical in the regulation of maternal and fetal vascular function during pregnancy and in the newborn. A decrease in PGI(2)/TXA(2) ratio in the maternal, fetal, and neonatal circulation may contribute to preeclampsia, intrauterine growth restriction, and persistent pulmonary hypertension of the newborn (PPHN), respectively. On the other hand, increased PGI(2) activity may contribute to patent ductus arteriosus (PDA) and intraventricular hemorrhage in premature newborns. These observations have raised interest in the use of COX inhibitors and PGI(2) analogs in the management of pregnancy-associated and neonatal vascular disorders. The use of aspirin to decrease TXA(2) synthesis has shown little benefit in preeclampsia, whereas indomethacin and ibuprofen are used effectively to close PDA in the premature newborn. PGI(2) analogs have been used effectively in primary pulmonary hypertension in adults and have shown promise in PPHN. Careful examination of PGI(2) metabolism and the complex interplay with other prostanoids will help design specific modulators of the PGI(2)-dependent pathways for the management of pregnancy-related and neonatal vascular disorders.