Andreas Baumbach

Local Paclitaxel Delivery for the Prevention of Restenosis: Biological Effects and Efficacy In Vivo

OBJECTIVE The aim of this study was to evaluate the potential of paclitaxel to prevent restenosis in vivo. BACKGROUND Paclitaxel (Taxol) is a microtubule-stabilizing compound with potent antitumor activity. It influences the cytoskeleton equilibrium by increasing the assembly of altered microtubules, thereby inducing cellular modifications that result in reduced proliferation, migration and signal transduction. METHODS Before the in vivo study, delivery efficiency was determined with radiolabeled paclitaxel in porcine hearts. After induction of a defined plaque in the right carotid arteries of 76 New Zealand rabbits by electrical stimulation, 27 animals underwent balloon dilation and subsequent local paclitaxel delivery (10 ml, 10 micromol/liter) with a double-balloon catheter. Twenty-nine animals served as control with angioplasty only, 10 animals underwent local delivery of vehicle only (0.9% NaCl solution) and 10 animals were solely electrostimulated. Vessels were excised one, four, and eight weeks after intervention. RESULTS The extent of stenosis in paclitaxel-treated animals was significantly reduced compared with balloon-dilated control animals (p = 0.0012, one, four and eight weeks after intervention: 14.6%, 24.6% and 20.5%, vs. 24.9%, 33.8% and 43.1%, respectively). Marked vessel enlargement compared with balloon-dilated control animals could be observed (p = 0.0001, total vessel area after one, four and eight weeks: paclitaxel group: 1.983, 1.700 and 1.602 mm2, control: 1.071, 1.338 and 1.206 mm2, respectively). Tubulin staining and electron microscopy revealed changes in microtubule assembly, which were limited to the intimal area. Vasocontractile function after paclitaxel treatment showed major impairment. CONCLUSIONS Local delivery of paclitaxel resulted in reduced neointimal stenosis and enlargement in vessel size. Both these effects contribute to a preservation of vessel shape and are likely to be caused by a structural alteration of the cytoskeleton.

Noninvasive determination of endothelium-mediated vasodilation as a screening test for coronary artery disease: Pilot study to assess the predictive value in comparison with angina pectoris, exercise electrocardiography, and myocardial perfusion imaging

BACKGROUND Peripheral endothelial dysfunction (ED) quantified by the determination of flow-mediated dilation (FMD%) of the brachial artery with the use of high-resolution ultrasound is an early marker of atherosclerosis. Although a positive correlation with coronary artery disease (CAD) has been reported, the unanswered clinical question is the validity of FMD% as a screening test in patients with clinical suspicion of CAD. Thus the aim of this study was to determine the predictive value of FMD% compared with angina pectoris, exercise electrocardiography, and myocardial perfusion imaging. METHODS AND RESULTS In this pilot study, we measured ED in 122 patients scheduled for coronary angiography by using high-resolution ultrasound (13 MHz). We defined ED as FMD% </=4.5%. The presence of CAD was defined as angiographically detectable atherosclerotic vessel alterations of any degree. Exercise electrocardiography and myocardial perfusion imaging had been performed on an outpatient basis. Statistical analysis was conducted by analysis of variance and Mantel-Haenszel chi-square test. Patients with CAD (n = 101) had a significantly lower FMD% than patients without CAD (n = 21; 3.7% +/- 4.1% vs 7.01% +/- 3.5%, P <.001). A sensitivity of 71%, a specificity of 81% with a positive predictive value of 0.95 (72 of 76), and a negative predictive value of 0.41 (17 of 46) was calculated. In comparison to angina pectoris (sensitivity 95%, specificity 47.6%), exercise electrocardiography (sensitivity 82.4%, specificity 57.1%) and myocardial perfusion imaging (sensitivity in our study group 100%) had the best specificity, and a high sensitivity for FMD% was found. CONCLUSIONS The determination of ED was found to be a sensitive and specific screening test to predict the presence of CAD. Because this is a noninvasive, nonradioactive, and cost-effective approach, it warrants further evaluation to determine its value in daily clinical practice as an additional screening test in the diagnosis of CAD.

Acute complications of excimer laser coronary angioplasty: A detailed analysis of multicenter results

OBJECTIVES The aim of this study was to document and analyze the incidence and consequences of complications of excimer laser coronary angioplasty. BACKGROUND Excimer laser coronary angioplasty has been reported to be a safe and feasible alternative or adjunct to conventional balloon angioplasty, but serious and unique complications have been observed. METHODS Data on 1,595 interventions of excimer laser coronary angioplasty in 1,521 patients were analyzed, using a merged data base from the U.S. and European Percutaneous Excimer Laser Coronary Angioplasty (PELCA) registries. RESULTS Procedural success was achieved in 89.3% of interventions. Stand-alone laser angioplasty was performed in 17.8% of interventions. Complications included dissection (22.0%), vasospasm (6.1%), filling defects (4.8%), abrupt reclosure (6.1%), embolization (2.3%), perforation (2.4%), arrhythmia (0.7%) and aneurysm formation (0.3%). Major complications were non-Q wave myocardial infarction (2.3%), Q wave myocardial infarction (1.0%), coronary artery bypass grafting (3.1%) and death (0.7%). Logistic regression analysis revealed correlation between dissections and the use of larger catheter size (p = 0.0005), high energy per pulse levels (p = 0.0001 for native vessels), lesion length > 10 mm (p = 0.001) and presence of a side branch (p = 0.01). The incidence of perforations was higher in women (p = 0.004), in treatment of total occlusions (p = 0.02) and in the presence of a side branch (p = 0.03). Fatal complications were correlated with patients with multivessel disease (p < 0.0001), patients with acute myocardial infarction (p = 0.0009) and older patients (> 70 years old, p = 0.004). The incidence of major complications decreased after performance of 50 laser angioplasty procedures at one institution (p = 0.02). CONCLUSIONS This analysis defines both the learning curve and the profile of complications for excimer laser angioplasty and provides insight into the selection of appropriate patients and proper performance of the procedure.

Local drug delivery: Impact of pressure, substance characteristics, and stenting on drug transfer into the arterial wall

Injection parameters for local drug delivery are frequently determined by studies with marker substances. However, the pharmacologic properties of the actual drug may influence delivery efficiency and lead to different results. Aim of this study was to assess the delivery capacities of two device‐drug combinations in order to verify this approach for further in vivo studies. Tritiated (3H) preparations (5 ml) of the hydrophylic low‐molecular‐weight heparin reviparin and the lipophilic taxane paclitaxel were injected into the left anterior descending artery of freshly explanted porcine hearts with the Infusasleeve II catheter system. A balloon support pressure of 6 atm and infusion pressures of 40, 60, 80, or 100 psi were used. In three additional groups, reviparin was injected following stent implantation and paclitaxel was injected prior to or following stent implantation. Arteries along with surrounding myocardium were harvested. The artery was carefully dissected, and artery and myocardium were separately homogenized, and activity was measured. Of the totally delivered activity, 0.09% ± 0.03% (40 psi) to 0.17% ± 0.13% (100 psi) of reviparin and 2.03% ± 0.67% (60 psi) to 2.68% ± 1.57% (100 psi) of paclitaxel were found in the vessel wall. The results for different injection pressures were not significantly different for either drug. The percentage activity delivered to the vessel wall was substantially larger in the paclitaxel group as compared to reviparin delivery (P < 0.01 at 60, 80, and 100 psi). The mean concentration of reviparin in the artery was 20 to 33 times higher than in the myocardium. For paclitaxel the factors were 110 to 243. Stent implantation prior to or following local delivery did not result in a different delivery efficiency. The results demonstrate that the characteristics of the delivered drug contribute largely to the delivery efficiency. Using identical injection parameters, drug concentrations in the arterial wall were significantly higher for the lipophilic paclitaxel as compared to the hydrophilic reviparin. Stenting of the artery did not influence delivery efficiency. Cathet. Cardiovasc. Intervent. 47:102–106, 1999.

Effect of exercise on valvular resistance in patients with mitral stenosis

OBJECTIVES This exercise study assessed the relation between valvular resistance and flow in patients with mitral stenosis. BACKGROUND Valvular resistance has been proposed as an alternative measure of stenotic valvular lesions, which is speculated to remain stable under changing hemodynamic conditions. METHODS In 35 of 40 patients with pure or predominant mitral stenosis, continuous wave Doppler measurements of the mitral stenotic jet were possible at rest and during supine bicycle ergometry. Simultaneously, transvalvular flow was assessed by thermodilution technique. For calculation of valvular resistance, the mean mitral valve pressure gradient was determined according to the simplified Bernoulli equation and divided by transvalvular flow. Additionally, effective mitral valve area was calculated according to the continuity equation method, dividing flow by the mean diastolic flow velocity. RESULTS Valvular resistance was 65 +/- 32 dynes.s.cm-5 at rest and increased to 82 +/- 43 dynes.s.cm-5 at 25 W (p < 0.001). The most prominent increase in valvular resistance (rest to 25 W 63 +/- 28 to 95 +/- 48 dynes.s.cm-5, p < 0.001) was found in those patients who had no or only a moderate (< 20%) change in effective mitral valve area. In contrast, valvular resistance remained constant (67 +/- 36 vs. 70 +/- 32 dynes.s.cm-5) in patients with a significant (> or = 20%) increase in mitral valve area with exercise. CONCLUSIONS In patients with mitral stenosis, the exercise-induced changes in valvular resistance are heterogeneous. This is the result of the variable response of mitral valve area to an increase in flow. In the individual patient, mitral valve area can significantly increase, a factor that has to be taken into account when interpreting the hemodynamic relevance of the obstruction. Calculated valvular resistance is flow dependent and has no advantage over valve area calculations for quantifying mitral stenosis.

Local drug delivery with porous balloons in the rabbit : Assessment of vascular injury for an improvement of application parameters

OBJECTIVES Sufficient intramural drug concentrations with the use of porous balloon catheters can be achieved with additional vascular trauma only. However, effective delivery of a potent drug even in deeper layers of the vessel wall might outweigh these traumatic side effects. Given the porous balloon catheter, the parameters of injection pressure and applied fluid volume will influence the interventional result. METHODS We tested a 2.5-mm porous balloon (35 75-micron pores) in the right carotid artery of New Zealand rabbits and used injection pressures of 1, 2, and 5 atm and fluid volumes of 2 and 4 ml of low-molecular-weight heparin solution in combination with the different parameters (n = 5 animals/group). In 50 rabbits, an intimal fibromuscular plaque was induced by using the electrostimulation model. Balloon dilatation and then application of the porous balloon was performed in 30 animals, 10 animals were only electrostimulated, and 10 animals served as a control group with balloon dilatation only. The vessels were excised 7 d after intervention, stained, and analyzed histomorpologically. Anti-Xa assays revealed the extent of systemically escaped drug, and serial cuts allowed for exact determination of vessel wall injuries. RESULTS Effective local drug delivery could not be achieved with an injection pressure of less than 2 atm. Specific pressure-driven effects such as jet injuries could be identified. When the pressure was high enough for disruptive drug delivery (> or = 2 atm), fluid volumes of 4 ml led to loose elastic membranes and local thickening within the media. CONCLUSIONS Sufficient intramural drug distribution using porous balloon catheters can be achieved with low injection pressures. Different fluid volumes strongly determine the extent of additional vascular injury.

Time course of smooth muscle cell proliferation after local drug delivery of low-molecular-weight heparin using a porous balloon catheter

It has been reported previously that systemic application of low molecular weight heparin (LMWH) suppresses smooth muscle cell (SMC) proliferation after balloon angioplasty in experimental studies. However, the high concentration of heparin required for a beneficial effect may cause severe bleeding complications. The ideal situation to overcome the systemic side effects would be to administer LMWH locally and deep into the arterial wall, which became possible by the development of porous balloon catheters. The in vivo feasibility of local delivery of LMWH using the porous balloon has been assessed by delivering tritium-marked LMWH into rabbit carotid arteries. The efficacy of the system was investigated by using a second injury animal model. After development of an intimal plaque by electrical stimulation, 61 rabbits were treated with the porous balloon after balloon angioplasty. In 23 rabbits, local drug delivery was accomplished with a porous balloon catheter (35 holes, hole diameter 75 microns, 2.5 mm catheter diameter). LMWH was locally administered with 4 ml (solution 375 anti-Xa-units/ml) and 2 atm. To study the extent of restenosis and morphological changes, these animals were killed 3, 7, 14, 28, or 56 d after intervention. After staining (hematoxylin, van Gieson, BrdU, RAM 11, alpha-actin) procedures to quantify SMC proliferation, intimal macrophages and morphological analysis were performed. Porous balloon treatment led to an increase in intimal SMC proliferation rate in the early stage after intervention. However, during the following time period, a significant decrease of the proliferation rate as compared with the animals treated with balloon angioplasty alone could be observed, which resulted in an only moderate increase of the intimal layer after local drug delivery compared with balloon angioplasty alone.

Paclitaxel: Ein Chemotherapeutikum zur Restenoseprophylaxe? Experimentelle Untersuchungen in vitro und in vivo

Paclitaxel, a potent anti-tumor agent, shifts the cytoskeleton equilibrium towards assembly of altered and extraordinarily stable microtubules. These cellular modifications lead to reduced proliferation, migration, and signal transduction. It is highly lipophilic, which promotes a rapid cellular uptake, and has a long-lasting effect in the cell due to the structural alteration of the cytoskeleton. This makes paclitaxel a promising candidate for local drug delivery intended to address the proliferative and migratory processes involved in restenosis. In this article, results of our in vitro and in vivo studies with paclitaxel are presented. Cell culture experiments with monocultures of human arterial smooth muscle cells as well as cocultures with human endothelial cells showed that paclitaxel leads to an almost complete growth inhibition within a dose range of 1.0–10.0μmol/l, even after a short (20 min) single dose application. The comparison of an active, semi-active, and passive delivery system (porous balloon, microporous balloon, and double balloon) favored the double balloon for the following in vivo experiments. Tubulin staining and electron microscopy enabled visualization of paclitaxel-induced vessel wall alterations. In the rabbit model, locally delivered paclitaxel resulted in reduced neointima formation and enlargement in vessel size; in the pig model, however, after stenting, this inhibition was not significant. Both reduced proliferation and enlargement in vessel size contribute to a preservation of vessel shape and are likely to be caused by a structural alteration of the cytoskeleton, which is also supported by vascular contraction force experiments. Paclitaxel, eine sehr potente antiproliferative Substanz, fördert die Bildung ungewöhnlich stabiler und funktionsgestörter Mikrotubuli und verändert dadurch zelluläre Mechanismen, die letztlich zu verminderter Proliferation, Migration und Signaltransduktion führen. Paclitaxel ist lipophil, was eine rasche Aufnahme in die Zelle fördert, und hat einen langanhaltenden Effekt in der Zelle aufgrund der strukturellen Veränderung des Zytoskelettes. Diese Eigenschaften machen Paclitaxel zu einem vielversprechenden Kandidaten für die lokale Medikamentenapplikation zur Restenoseprophylaxe. In dieser Arbeit werden die in-vitro und in-vivo Ergebnisse aus unseren Forschungsarbeiten zu Paclitaxel vorgestellt. Zellkulturexperimente mit Monokulturen von humanen glatten Gefäßmuskelzellen sowie mit Co-Kulturen mit humanen Endothelzellen zeigten, daß Paclitaxel in einem Dosisbereich zwischen 1,0 und 10,0μmol/l zu einer beinahe vollständigen Wachstumshemmung, selbst nach kurzer (20 min.) Einmalapplikation führt. Nach Vergleich von 3 verschiedenen Kathetersystemen (poröser Ballon, mikroporöser Ballon und Doppelballon) wurde der Doppelballon für die in-vivo Anwendung favorisiert. Anhand von Anfärbungen des Zytoskelettes sowie elektronenoptisch gelang der Nachweis der Paclitaxelwirkung in den glatten Muskelzellen der Gefäßwand. Im Kaninchen führte lokal appliziertes Paclitaxel zu einer signifikanten Hemmung der neointimalen Proliferation und Erweiterung des Gefäßdurchmessers im Vergleich zu ballondilatierten Kontrolltieren. In Zusatzexperimenten konnte eine drastische Verringerung der vaskulären Kontraktionskraft nach Paclitaxelgabe gezeigt werden. Ähnlich eindeutige Ergebnisse fanden sich nach Stentimplantation im Schweinemodell nicht.

Fibrin specificity and procoagulant effect related to the kallikrein-contact phase system and to plasmin generation with double-bolus reteplase and front-loaded alteplase thrombolysis in acute myocardial infarction.

This study was undertaken to compare the effects of reteplase and alteplase regimens on hemostasis and fibrinolysis in acute myocardial infarction (AMI). Thrombolytic treatment in patients with AMI is hampered by paradoxical procoagulant effects that favor early reocclusion. In vivo data comparing this effect and the fibrin specificity of double-bolus reteplase and front-loaded alteplase regimens are not available. In a prospective, randomized study, 50 patients with AMI were either treated with double bolus (10 + 10 U) reteplase or with front-loaded alteplase (up to 100 mg) within 6 hours of symptom onset. Thirty apparently healthy persons served as controls. Molecular markers of coagulation and fibrinolysis were serially examined for up to 5 days. Paradoxical thrombin activation at 3 hours after initiation of therapy was comparable between reteplase and alteplase. Reteplase (65 +/- 5 U/L) and alteplase (72 +/- 8 U/L) caused significantly elevated kallikrein activity at 3 hours after adminstration (p <0.01 vs controls 30 +/- 1 U/L). Fibrin specificity was less for reteplase (p <0.05) with a decrease in fibrinogen at 3 hours to 122 +/- 27 mg/dl versus 224 +/- 28 mg/dl for alteplase (p <0.01 and p <0.05 vs controls). D-Dimer levels at 3 hours were higher (p <0.05) after reteplase (5,459 +/- 611 ng/ml) versus alteplase (3,445 +/- 679 ng/ml) (both p <0.01 vs controls 243 +/- 17 ng/ml). Plasmin generation (plasmin-antiplasmin complexes) was significantly (p <0.01) increased at 3 hours with both regimens to 27,079 +/- 3,964 microg/L (reteplase) and 19,522 +/- 2,381 microg/L (alteplase). The data from 3 hours after start of thrombolytic therapy proved less marked fibrin specificity of the reteplase regimen (in vivo) compared with front-loaded alteplase. Both regimens have a moderate procoagulant effect without differences in activation of the kallikrein system.

Visualization and comparison of drug effects after local paclitaxel delivery with different catheter types

AbstractBackground: The microtubule stabilizing compound paclitaxel has proved to have potent antiproliferative effects on smooth muscle cells both in vitro and in vivo. It induces cellular modifications that result in reduced proliferation, migration and signal transduction by shifting the cellular microtubule equilibrium towards assembly. We therefore reasoned that a visualization of the altered cytoskeleton could enable an evaluation of the drug effects following local drug delivery. Methods and results: 3 catheters – the porous balloon, the microporous balloon and the double balloon catheter – were chosen for this study representing the spectrum from passive to active, pressure-driven delivery. After the induction of a defined plaque in the right carotid arteries of 40 New Zealand rabbits by electrical stimulation, 32 animals underwent balloon dilatation and 8 animals served as pre-interventional control group with electrostimulation only. In 24 animals (n = 8 in each group) subsequent local paclitaxel delivery (10 μmol/L) was performed. 8 animals served as control with angioplasty only. Vessels were excised 1 week following intervention. Immunohistochemistry with antibodies against bromodeoxyuridine, alpha-actin, macrophages, von Willebrand factor and α-tubulin was performed. Cytoskeletal changes were analyzed by electron microscopy. Tubulin staining and electron microscopy revealed changes with distinct staining patterns for the different catheters. Specific catheter-induced injuries could be identified for the porous and double balloon catheter. Intimal proliferation, percentage of macrophages and extent of injury favor the double balloon catheter for local paclitaxel delivery. Conclusions: The alterations of the cytoskeleton induced by paclitaxel allowed for the detection of drug action by staining of tubulin and electron microscopy. This enables an evaluation of transfer, distribution and drug effects directly in the vasculature without marker substances. The double balloon catheter appears to be best suited for local paclitaxel therapy.