Synchrotron microtomography reveals insights into the degradation kinetics of bio-degradable coronary magnesium scaffolds

Bioresorbable magnesium scaffolds are a promising future treatment option for coronary artery stenosis, especially for young adults. Due to the degradation of these scaffolds (<1 year), long-term device-related clinical events could be reduced compared to treatments with conventional drug eluting stents. First clinical trials indicate a return of vasomotion after one year, which may be associated with improved long-term clinical outcomes. However, even after decades of development, the degradation process, ideal degradation time and biological response in vivo are still not fully understood. The present study investigates the in vivo degradation of magnesium scaffolds in the coronary arteries of pigs influenced by different strut thicknesses and the presence of antiproliferative drugs. Due to high 3D image contrast of synchrotron-based micro-CT with phase contrast (SR-μCT), a qualitative and quantitative evaluation of the degradation morphology of magnesium scaffolds was obtained. For the segmentation of the μCT images a convolutional network architecture (U-net) was exploited, demonstrating the huge potential of merging high resolution SR-μCT with deep learning (DL) supported data analysis. In total, 30 scaffolds, made of the rare earth alloy Resoloy®, with different strut designs were implanted into the coronary arteries of 10 domestic pigs for 28 days using drug-coated or uncoated angioplasty balloons for post-dilatation. The degradation morphology was analyzed using scanning electron microscopy, energy dispersive x-ray spectroscopy and SR-μCT. The data from these methods were then related to data from angiography, optical coherence tomography and histology. A thinner strut size (95 vs. 130 μm) and the presence of paclitaxel indicated a slower degradation rate at 28 d in vivo, which positively influences the late lumen loss (0.5 and 0.6 mm vs. 1.0 and 1.1 mm) and recoil values (0 and 1.7% vs. 6.1 and 22%).

One single drug-coated balloon for all shapes/diameters? Neointimal proliferation inhibition in porcine peripheral arteries

BACKGROUND

Long diseased vessel segments of peripheral arteries may display irregular shapes with different diameters. The aim of this study was to investigate inhibition of neointimal proliferation in porcine peripheral vessels with different diameters covered by one single hyper-compliant drug-coated balloon (HCDCB), compared to conventional drug-coated balloons (DCB), each selected according to the respective vessel diameter.

METHODS AND RESULTS

Neointimal proliferation was stimulated in proximal and distal segments of the peripheral arteries by balloon overstretch and stent implantation. Inhibition of neointimal proliferation by one single HCDCB was compared to two vessel diameter-adjusted DCB per artery and to one single uncoated hyper-compliant balloon (HCB). Sixteen HCB, 16 HCDCB, and 32 DCB were used in 16 arteries each. Quantitative angiography (QA), optical coherence tomography (OCT) and histology showed a similar anti-restenotic effect for one HCDCB compared to two vessel diameter-adjusted DCB in narrow distal and wider proximal segments (QA diameter stenosis: 18.7±12.3% vs. 22.8±15.5%, p = 0.535; OCT area stenosis: 21.4±11.6% vs. 23.6±12.3%, p = 0.850; histomorphometry diameter stenosis: 27.5±7.1% vs. 26.9±8.0%, p = 0.952) and indicated significant inhibition of neointimal proliferation by HCDCB vs. uncoated HCB (QA diameter stenosis: 18.7±12.3% vs. 30.3±16.7%, p = 0.008; OCT area stenosis: 21.4±11.6% vs. 34.7±16.0%, p = 0.004; histomorphometry diameter stenosis: 27.5±7.1% vs. 32.5±8.5%, p = 0.038).

CONCLUSIONS

HCDCB were found to be similar effective as DCB in inhibiting neointimal proliferation in vessel segments with different diameters. One single long HCDCB may allow for treatment of segments with variable diameters, and thus, replace the use of several vessel diameter-adjusted DCB.

Drug-Coated Balloons: Drugs Beyond Paclitaxel?

BACKGROUND

Although controversially discussed, paclitaxel is the only clinically proven drug that inhibits restenosis when released from drug-coated balloons (DCBs). Limus drugs are currently being explored as alternatives. The aim of the preclinical studies was to investigate drug candidates beyond paclitaxel considered for balloon coating.

METHODS

Drugs were tested with respect to dissolution in organic solvents, coating on balloons, and drug transfer to the vessel wall. Inhibition of neointimal proliferation was tested in the porcine model of coronary in-stent stenosis. Intravascular drug treatment was achieved by DCBs at the time of stent implantation.

RESULTS

Coating had to be adjusted for each drug. Doses on the balloons ranged from 1.0 to 8.6 μg/mm2 balloon surface. Satisfactory amounts of drug ranging from 5% to 29% of initial doses were transferred into the vessel wall. Angiographic parameters such as late lumen loss (LLL) at 4 weeks did not show reduction of in-stent neointimal proliferation by treatment with arsenic trioxide (0.87 ± 0.44 mm), betamethasone dipropionate (1.00 ± 0.54 mm), bortezomib (1.74 ± 0.46 mm), green tea extract (1.24 ± 0.51 mm), fantolon, an epothilone (0.86 ± 0.61 mm), methotrexate (1.09 ± 0.72 mm), and thalidomide (1.59 ± 0.55 mm) compared to treatment with uncoated balloons (1.07 ± 0.60 mm), while coatings with paclitaxel reliably reduced in-stent stenosis (LLL = 0.36 ± 0.25 mm).

CONCLUSIONS

Despite the proven antiproliferative and/or anti-inflammatory effect of the drugs, none of the coatings significantly reduced LLL compared to uncoated balloons and thus, based on the results presented here, none of the tested coatings may be considered a substitute for the paclitaxel-based coatings currently in clinical use.

Improvement of Outcome for Treatment of ‘Restenosis-prone’ Vascular Lesions? Potential Impact of the Paclitaxel dose on Late Lumen Loss in Porcine Peripheral Arteries

Purpose

Clinical data indicate that the drug density on drug-coated balloons (DCBs) might have a role on treatment effect and durability. The aim of the current study was to investigate inhibition of neointimal formation and potential adverse effects after treatment with a novel double-dose DCB in swine.

Material and methods

A four-week study was performed in peripheral arteries of 12 domestic pigs after vessel injury and stent implantation. The novel double-dose DCB with 6-µg paclitaxel (Ptx)/mm2 balloon surface (1 × 6) was compared to a standard DCB with 3.5 µg Ptx/mm2 (3.5) and uncoated balloons (POBA). Potential adverse effects were stimulated by using three fully overlapping DCBs with 6 µg Ptx/mm2 each (3 × 6). Quantitative angiography, histomorphometry and histopathological analyses were performed.

Results

Higher paclitaxel doses per square millimeter of treated arteries were associated with reduced late lumen loss (LLL) in quantitative angiography 4 weeks after treatment (POBA: 0.91 ± 0.75 mm; 3.5: 0.45 ± 0.53 mm; 1 × 6: 0.21 ± 0.41 mm; 3 × 6: − 0.38 ± 0.65 mm). In histomorphometry, maximal neointimal thickness and neointimal area were the lowest for the 1 × 6 group (0.15 ± 0.06 mm/1.5 ± 0.4 mm2), followed by 3 × 6 (0.20 ± 0.07 mm/1.8 ± 0.4 mm2), 3.5 (0.22 ± 0.12 mm/2.2 ± 1.1 mm2) and POBA (0.30 ± 0.07 mm/3.2 ± 0.7 mm2). Downstream tissue showed histopathological changes in all groups including POBA, in larger number and different quality (e.g., edema, inflammation, vessel wall necrosis, vasculitis and perivasculitis) in the 3 × 6 group, which did not cause clinical or functional abnormalities throughout the study.

Conclusion

Treatment with the double-dose DCB (6 µg Ptx/mm2) tended to increase inhibition of in-stent neointimal formation and to diminish LLL after peripheral intervention in the porcine model compared to a market-approved DCB with 3.5 µg Ptx/mm2.

Preclinical Evaluation of the Temporary Drug-Coated Spur Stent System in Porcine Peripheral Arteries

BACKGROUND

Drug penetration into the deeper arterial wall of heavily calcified lesions is one of the limitations of drug-coated balloons and drug-eluting stents in vascular interventions. The Temporary Spur Stent (TSS) system is characterized by a self-expanding nitinol stent that is uniformly covered in radialspikes, which, when coated, should allow a deeper penetration and longer retention of the drug into the diseased artery walls by penetrating through the calcified plaques.

MATERIALS AND METHODS AND RESULTS

Uncoated TSS and paclitaxel (PTX)-coated TSS systems have been deployed in porcine peripheral arteries. Four weeks after the deployment of uncoated TSS systems, no adverse vascular remodeling or neointimal formation in the treated vessel segments were noticed. PTX-coated TSS systems transferred 9%±7% of the drug that was on the device to the targeted vessel area (196±163 ng PTX/mg arterial tissue) and the addition of the fluorescent dye Nile red to the coating showed that the spikes promote the transfer of the coating to the deeper layers of the vessel wall. The PTX-coated TSS systems showed a significant reduction in neointimal proliferation compared to the uncoated TSS systems: quantitative angiography showed a vessel diameter stenosis of 37.2%±11.0% and 16.4%±8.8% 4 weeks after the treatment with uncoated and PTX-coated TSS systems, respectively.

CONCLUSION

The treatment with the TSS system was well tolerated and the spikesfacilitate the transfer of the coating into deeper layers of the vessel wall. Moreover, the PTX-coated TSS systems effectively inhibit neointimal proliferation.

Efficacy and safety of a magnesium stearate paclitaxel coated balloon catheter in the porcine coronary model

BACKGROUND

Local administration of growth-inhibiting substances such as paclitaxel or sirolimus could reduce the risk of restenosis. In the drug coated balloon (DCB) technology the coating and the applied dose seem to play a major role. The aim of the present preclinical studies was to investigate the efficacy and safety of a specific DCB with paclitaxel as active ingredient and magnesium stearate as excipient.

METHODS

Evaluation of the coating, drug release and transfer was done ex vivo and in vivo on peripheral arteries. A porcine coronary stent model was chosen to provoke intimal thickening. Conventional uncoated balloons were compared with paclitaxel urea and paclitaxel magnesium stearate coated balloons. QCA and histomorphometry was performed on treated vessels. Three areas of the heart were histologically examined for pathological changes.

RESULTS

QCA and histomorphometry revealed no differences in baseline data between treatment groups. All DCB groups showed a significant reduction of angiographic and histologic parameters describing neointimal formation 4 weeks after treatment (e.g. mean angiographic late lumen loss all coated 0.31 ± 0.18 mm versus 0.91 ± 0.37 mm in the uncoated balloon group). There were no device-related animal deaths or clinical abnormalities. In spite of very slight-to-slight microscopic findings limited to small arterial vessels in downstream tissue there was no change in left ventricular ejection fraction or angiographic presentation of small side branches of treated arteries.

CONCLUSION

Paclitaxel DCB using stearate as excipient show a high efficacy in reducing neointima formation after experimental coronary intervention. No evidence of myocardial damage resulting from distal embolization was found.

Novel, vessel anatomy adjusting drug-coated balloon-Preclinical evaluation in peripheral porcine arteries

BACKGROUND

The diameter of balloons or stents is selected according to the estimated reference vessel diameter and do not adapt to the vessel anatomy. The aim of the present preclinical studies was to investigate a novel, vessel anatomy adjusting hypercompliant drug-coated balloon catheter (HCDCB).

METHODS

Hypercompliant balloon membranes were coated in a constricted state with high drug density. Drug adherence was investigated in vitro, transfer to the porcine peripheral arteries and longitudinal distribution in vivo. In young domestic swine, neointimal proliferation was induced by vessel overstretch and continuous irritation by permanent stents. Uncoated hypercompliant balloons (HCB), and standard uncoated balloons and drug-coated balloons (DCB) served as controls. Efficacy was assessed by angiography, optical coherence tomography (OCT), and histomorphometry.

RESULTS

HCDCB lost 18.0 ± 3.9% of dose during in vitro simulated delivery to the lesion. Drug transfer to the vessel wall was 13.9 ± 6.4% and drug concentration was 1,044 ± 529 ng/mg tissue. Four weeks after treatment, the histomorphometric neointimal area was smaller with HCDCB versus uncoated HCB (2.39 ± 0.55 mm² vs. 3.26 ± 0.72 mm² , p = .038) and area stenosis (OCT) was less (11.6 ± 6.9% vs. 24.7 ± 9.7%, p = .022). No premature death occurred and no in-life clinical symptoms or treatment-associated thrombi were observed.

CONCLUSIONS

HCDCB were found to inhibit excessive neointimal proliferation. Balloon adaption to different vessel diameters and shapes may provide drug-delivery in irregular lumen and facilitate balloon selection.

Drug Distribution and Basic Pharmacology of Paclitaxel/Resveratrol-Coated Balloon Catheters

Purpose

To experimentally investigate a new homogenously paclitaxel/resveratrol-coated balloon catheter in terms of transport of the coating to the treated tissue and local effects including histology and functional tests.

Methods

Adherence of the coating to the balloon was explored by in vitro simulation of its passage to the lesion. Paclitaxel and resveratrol transfer to the vessel wall was investigated in porcine coronary and peripheral arteries. Matrix-assisted laser desorption/ionization (MALDI) was used for direct microscopic visualization of paclitaxel in arterial tissue. Inhibition of neointimal proliferation and tolerance of complete coating and resveratrol-only coating was investigated in pigs 4 weeks after treatment, and the effect of resveratrol on inflammation and healing after 3 and 7 days.

Results

Drug loss on the way to the lesion was < 10% of dose, while 65 ± 13% was detected at the site of balloon inflation. After treatment similar proportions of drug were detected in coronary and peripheral arteries, i.e., 7.4 ± 4.6% of dose or 125 ± 74 ng/mg tissue. MALDI showed circumferential deposition. Inhibition of neointimal proliferation by paclitaxel/resveratrol coating was significant (p = 0.001) whereas resveratrol-only coating did not inhibit neointimal proliferation. During the first week after treatment of peripheral arteries with resveratrol-only balloons, we observed nominally less inflammation and fibrin deposition along with a significant macrophage reduction and more pronounced re-endothelialization. No safety issues emerged including left ventricular ejection fraction for detection of potential distal embolization after high-dose treatment of coronary arteries.

Conclusions

Paclitaxel/resveratrol-coated balloons were effective and safe in animal studies. Beyond acting as excipient resveratrol may contribute to vascular healing.

Novel Sirolimus–Coated Balloon Catheter

Background—

Limus-eluting stents are dominating coronary interventions, although paclitaxel is the only drug on balloon catheters with proven inhibition of restenosis. Neointimal inhibition by limus-coated balloons has been shown in few animal studies, but data from randomized clinical trials are not available. The aim of the present preclinical studies was to achieve high and persistent sirolimus levels in the vessel wall after administration by a coated balloon.

Methods and Results—

Different coating formulations and doses were studied in the porcine coronary model to investigate sirolimus tissue levels at different time points as well as efficacy at 1 month using quantitative coronary angiography and histomorphometry. Loss of the selected coating in the valve, guiding catheter, and blood was low (2±14% of dose). Acute drug transfer to the vessel wall was 14.4±4.6% with the crystalline coating, whereas the amorphous coatings were less effective in this respect. Persistence of sirolimus in the vessel wall until 1 month was 40% to 50% of the transferred drug. At 1-month follow-up, a modest but significant reduction of neointimal growth was demonstrated in a dose range from 4 μg/mm 2 to 2×7 μg/mm 2 , for example, maximum neointimal thickness of 0.38±0.13 versus 0.65±0.21 mm in the uncoated control group.

Conclusions—

Various sirolimus-coated balloons effectively reduce neointimal proliferation in the porcine coronary model but differ considerably in retention time in the vessel wall. It has to be determined if such a formulation with persistent high vessel concentration will result in a relevant clinical effect.

Differential chemokine receptor expression regulates functional specialization of endothelial progenitor cell subpopulations

Postnatal vasculogenesis is mediated by endothelial progenitor cells (EPCs) which consist of subpopulations with different functional capacities. Our goal was to profile chemokine receptor expression on relevant subsets of EPCs and to characterize their role for effector functions. CD34(+)/CD133(+)/VEGFR2(+) EPCs were characterized by high expression of chemokine receptors CXCR4, CX3CR1, BLT1, and low level expression of CXCR2 and CCR2, while primordial CD34(-)/CD133(+)/VEGFR2(+) EPCs express these chemokine receptors at comparably low levels. Migration assays revealed that SDF-1, fractalkine, and LTB4 significantly increase migration of CD34(-)/CD133(+)/VEGFR2(+) EPCs, while SDF-1 was the only potent agonist of migration of CD34(+)/CD133(+)/VEGFR2(+) EPCs. SDF-1, fractalkine, and LTB4 trigger significant increase adhesion of CD34(+)/CD133(+)/VEGFR2(+) EPCs, while in CD34(-)/CD133(+)/VEGFR2(+) EPCs SDF-1 and fractalkine are equipotent agonists and LTB4 triggers a smaller though still significant increase in adhesion. Differential expression of specific chemokine receptors is an important regulator in terms of migration and adhesion of biologically relevant EPC-subpopulations, which may have implications for cell therapeutic strategies for treatment of ischemic vascular disease.

Genetic heterogeneity of prostatic carcinoma-derived cell lines as emphasized by DNA fingerprinting

To investigate genetic heterogeneity during in vitro cultivation of human prostatic carcinomas following radical prostatectomy we performed DNA fingerprinting using the digoxygenin-labeled probes (GACA)4 and (GTG)5. DNA was isolated from fresh material stemming from different areas within one tumor and from cell cultures of the same material. The patterns which were obtained by the nucleolar organizer region (NOR)-specific probe (GACA)4 exhibit only a few prominent low molecular mass bands and no differences were observed between any of the tumors analyzed so far. Changes in the fingerprint pattern occurred between cell cultures derived from different areas within one tumor when the DNA was cleaved by HaeIII and signals detected with the (GTG)5 probe. The "area-specific" pattern was stable during several subcultivations of these cell lines, indicating genetic stability of these prostatic carcinoma cells in vitro. Thus individual cell lines derived from radical prostatectomy seem to represent a biological system very close to the situation in vivo.