Restenosis--an open file

Influence of unsaturated carbonic acids on hemocompatibility and cytotoxicity of poly-vinylacetate based co-polymers

The aim of this study was to investigate hemocompatibility and cytotoxicity properties of synthetic polymer coatings containing various unsaturated carbonic acids with vinylacetate. Co-polymers of vinylacetate and crotonic acid (CA), maleic acid (MA), and itaconic acid (IA) were made. The materials were characterized in terms of their adhesion to metal supports (titanium and stainless steel) as well as hemocompatibility (% hemolysis, wettability, erythrocyte aggregation, hemoglobin content, thrombocyte count and lipid peroxidation levels) and cytotoxicity (human endothelial cell activity in vitro and chromosome aberrations, bone marrow proliferation and cell ploidy in rats). Co-polymers of unsaturated carbonic acids with vinylacetate exhibited good hemocompatibility properties, as opposed to vinylacetate homopolymer for which substantial levels of hemolysis were observed. By coating the metal supports with co-polymers the cytotoxic effects associated with the bare metal samples were markedly reduced. MA samples showed excellent hemocompatibility and no cytotoxicity, yet they lacked good adhesion properties to metal substrate, probably due to high water content. CA samples, having the highest density of carboxylic groups among the samples under investigation, showed increased bone marrow proliferation activity and cell ploidy in rats, as compared to controls. The most promising results in the present study were obtained for the samples with IA, which showed good adhesion to metal substrates, good hemocompatibility and low cytotoxicity. Thus, co-polymers of vinylacetate and IA rich in carboxylic groups are promising materials for the design of novel drug-eluting stents.

Coronary stents: a materials perspective

The objective of this review is to describe the suitability of different biomaterials as coronary stents. This review focuses on the following topics: (1) different materials used for stents, (2) surface characteristics that influence stent-biology interactions, (3) the use of polymers in stents, and (4) drug-eluting stents, especially those that are commercially available.

Adventitial response to intravascular brachytherapy in a rabbit model of restenosis

BACKGROUND

The incidence of late major adverse cardiac events (MACE) after coronary brachytherapy is higher than in controls. Because expansive remodeling has been shown to correlate with poor clinical outcome after vascular interventions, we studied adventitial changes after intravascular irradiation in a rabbit model.

METHODS

Twenty normolipidemic rabbits underwent balloon injury in both external iliac arteries. One artery was assigned for subsequent irradiation with a 90Y source (15 Gy or 30 Gy at 0.5 mm in the vessel wall). After four weeks morphometric measurements were made and cell density and collagen amount determined. Staining for Ki67 identified proliferating cells; apoptotic cells were identified by TUNEL staining. Proliferative and apoptotic indices were calculated as the number of respective positive cells/total cell count x100.

RESULTS

The neointimal area decreased to 0.27 +/- 0.3 mm2 after irradiation compared with 0.55 +/- 0.2 mm2 in controls (p=0.007), whereas adventitial area increased from 0.62 +/- 0.3 mm2 to 0.87 +/- 0.3 mm2 (p=0.02). Irradiation reduced both the proliferative (0.95 +/- 2.6 vs. 3.73 +/- 4.7, p=0.026) and apoptotic (0.006 +/- 0.02 vs. 0.107 +/- 0.2, p=0.03) indices in the neointima, but not in the other arterial-wall layers. Collagen amount and arterial remodeling did not differ between the groups. There was no difference between 15 and 30 Gy in any of the parameters, although adventitial thickening was more pronounced in the high-dose group.

CONCLUSIONS

In normolipidemic rabbits, intravascular beta-irradiation after balloon angioplasty is associated with an increase in neoadventitia and a reduction of neointima. It is conceivable that this phenomenon may contribute to the increased incidence of late MACE after vascular brachytherapy.

Mechanical behavior of coronary stents investigated through the finite element method

Intravascular stents are small tube-like structures expanded into stenotic arteries to restore blood flow perfusion to the downstream tissues. The stent is mounted on a balloon catheter and delivered to the site of blockage. When the balloon is inflated, the stent expands and is pressed against the inner wall of the coronary artery. After the balloon is deflated and removed, the stent remains in place, keeping the artery open. Hence, the stent expansion defines the effectiveness of the surgical procedure: it depends on the stent geometry, it includes large displacements and deformations and material non-linearity. In this paper, the finite element method is applied (i) to understand the effects of different geometrical parameters (thickness, metal-to-artery surface ratio, longitudinal and radial cut lengths) of a typical diamond-shaped coronary stent on the device mechanical performance, (ii) to compare the response of different actual stent models when loaded by internal pressure and (iii) to collect suggestions for optimizing the device shape and performance. The stent expansion and partial recoil under balloon inflation and deflation were simulated. Results showed the influence of the geometry on the stent behavior: a stent with a low metal-to-artery surface ratio has a higher radial and longitudinal recoil, but a lower dogboning. The thickness influences the stent performance in terms of foreshortening, longitudinal recoil and dogboning. In conclusion, a finite element analysis similar to the one herewith proposed could help in designing new stents or analyzing actual stents to ensure ideal expansion and structural integrity, substituting in vitro experiments often difficult and unpractical.

Intravascular brachytherapy of the coronary arteries

This is a review of the relatively recently developed field of intravascular brachytherapy of coronary arteries. It presents a brief overview of the discipline of coronary angioplasty describing the problem of restenosis and discusses the potential for ionizing radiation to overcome this problem. It examines the various methods that have been used to irradiate the coronary arteries comparing their advantages and disadvantages. Special consideration is given to seeds and wires in the artery, radioactive liquids in the angioplasty balloon and radioactive stents. Passing reference is made to a number of other methods that have also been proposed, but which are not commonly used to irradiate the coronary arteries at present. The dosimetry of each of the major techniques is discussed and the data from different laboratories compared. Specific consideration is given to the need for centring of the radioactive source and the factors affecting the selection of a dose prescription. A brief review of recent clinical trials is followed by an examination of possible future directions in this field including the use of intravascular ultrasound to improve dosimetry, the use of gas-filled balloons to enhance the penetration of beta-emitting sources and the use of gamma-emitting stents to overcome the problems associated with edge restenosis.

Local delivery of mithramycin restores vascular reactivity and inhibits neointimal formation in injured arteries and vascular grafts

Arterial restenosis is responsible for the high failure rates of vascular reconstruction procedures. Local sustained drug delivery has shown promise in the prevention of restenosis. The drug release rate from mithramycin-loaded EVA matrices (0.1%) was evaluated, and their antirestenotic effect was studied in the rat carotid model and rabbit model of vascular grafts. The modulation of c-myc expression by mithramycin treatment was examined by immunohistochemistry in the rat carotid model. The proliferative response of injured rat arteries was studied by bromdeoxyuridine (BrdU) immunostaining. The impact of mithramycin treatment on vasomotor responses of the venous segments grafted into arterial circulation was studied ex vivo using vasoreactive compounds. Mithramycin was released exponentially from EVA matrices in PBS. Matrices co-formulated with PEG-4600 revealed enhanced release kinetics. The perivascular implantation of drug-loaded EVA-PEG matrices led to 50% reduction of neointimal formation, and reduced the c-myc expression and BrdU labeling in comparison to control implants. Decreased sensitivity of mithramycin-treated grafts to serotonin-induced vasoconstriction was observed. Local perivascular mithramycin treatment limits the functional alteration caused by the grafting of venous segments in high-pressure arterial environment, and potently inhibits stenosis secondary to grafting and angioplasty injury. The antirestenotic effect is associated with reduced c-myc expression and with subsequent decrease in SMC proliferation.

Dose–volume histograms based on serial intravascular ultrasound: a calculation model for radioactive stents

BACKGROUND AND PURPOSE

Radioactive stents are under investigation for reduction of coronary restenosis. However, the actual dose delivered to specific parts of the coronary artery wall based on the individual vessel anatomy has not been determined so far. Dose-volume histograms (DVHs) permit an estimation of the actual dose absorbed by the target volume. We present a method to calculate DVHs based on intravascular ultrasound (IVUS) measurements to determine the dose distribution within the vessel wall.

MATERIALS AND METHODS

Ten patients were studied by intravascular ultrasound after radioactive stenting (BX Stent, P-32, 15-mm length) to obtain tomographic cross-sections of the treated segments. We developed a computer algorithm using the actual dose distribution of the stent to calculate differential and cumulative DVHs. The minimal target dose, the mean target dose, the minimal doses delivered to 10 and 90% of the adventitia (DV10, DV90), and the percentage of volume receiving a reference dose at 0.5 mm from the stent surface cumulated over 28 days were derived from the DVH plots. Results were expressed as mean+/-SD.

RESULTS

The mean activity of the stents was 438+/-140 kBq at implantation. The mean reference dose was 111+/-35 Gy, whereas the calculated mean target dose within the adventitia along the stent was 68+/-20 Gy. On average, DV90 and DV10 were 33+/-9 Gy and 117+/-41 Gy, respectively. Expanding the target volume to include 2.5-mm-long segments at the proximal and distal ends of the stent, the calculated mean target dose decreased to 55+/-17 Gy, and DV 90 and DV 10 were 6.4+/-2.4 Gy and 107+/-36 Gy, respectively.

CONCLUSIONS

The assessment of DVHs seems in principle to be a valuable tool for both prospective and retrospective analysis of dose-distribution of radioactive stents. It may provide the basis to adapt treatment planning in coronary brachytherapy to the common standards of radiotherapy.

Mechanisms in the inhibition of neointimal hyperplasia with triflavin in a rat model of balloon angioplasty

RGD-containing peptides are able to inhibit the binding of ligands to certain beta3 integrins, such as alpha(IIb)beta3 and alpha(v)beta3, both of which are involved in neointimal hyperplasia. The present study was designed to elucidate the detailed mechanisms involved in the inhibition of neointimal hyperplasia with triflavin in a rat model of balloon angioplasty. Triflavin (0.25 mg x kg(-1) x d(-1)), an RGD-containing disintegrin, time dependently inhibited both neointimal hyperplasia and lumen occlusion after angioplasty in carotid arteries of rats. Furthermore, electron micrographs highlighted that SMCs were phenotypically different from the typical contractile, spindle-shaped SMCs normally seen in uninjured vessel walls. PDGF-BB was strongly produced in thrombus formation and neointimal SMCs after angioplasty, and triflavin significantly reduced PDGF-BB expression in vessel lumens and neointimal SMCs after angioplasty. Balloon angioplasty caused a significant increase of nitrate and cyclic guanosine monophosphate levels compared with levels found in sham-operated rats, and these were not significantly changed with infusion of triflavin (0.25 mg x kg(-1) x d(-1)). Furthermore, the plasma level of TXB2 obviously increased after angioplasty, and triflavin markedly suppressed the elevation of plasma TXB2 concentration. The results indicate that triflavin effectively prevents neointimal hyperplasia, possibly through the following 2 mechanisms. First, triflavin binds to alpha(IIb)beta3 integrin on platelet membranes, resulting in inhibition of platelet adhesion, secretion, and aggregation in injured arteries, followed by inhibition of TXA2 formation and PDGF-BB release from platelets. Second, triflavin may also bind to alpha(v)beta3 integrin on SMCs, thus subsequently inhibiting cell migration and proliferation. These results provide new insights into the mechanisms of neointimal hyperplasia and have significant implications for disintegrin therapy for the treatment of restenosis and atherosclerosis.

Restenosis after Angioplasty

Angiographic restenosis occurs in 30% to 50% of patients after percutaneous transluminal coronary angioplasty (PTCA) with 20% to 30% target vessel revascularization at one year, and is associated with increased morbidity, mortality and health care costs. Intracoronary stents are the first line of therapy against restenosis after angioplasty. Depending on lesion morphology and location, stents can reduce restenosis and target lesion revascularization (TLR) by 20% to 30%. Obstructive coronary lesions in vessels with a diameter larger than 3.0 mm should be stented. The benefit of stenting in vessels smaller than 3.0 mm is controversial, with the BESMART (Bestent in Small Arteries) and ISAR-SMART (Intracoronary Stenting or Angioplasty for Restenosis Reduction in Small Arteries) studies demonstrating conflicting results. Chronically occluded and subtotal vessels should be stented after PTCA. Obstructive lesions in saphenous vein grafts should be stented. It is preferable to stent ostial lesions after PTCA. Restenosis can occur in 15% to 25% of patients within 6 months of stent placement. Initial approach to focal in-stent restenosis is to repeat PTCA. Patients with diffuse restenosis may require debulking prior to PTCA to improve acute results. "Stenting within-stent" has not proven beneficial unless there is diffuse in-stent restenosis, neointimal prolapse or vessel dissection during PTCA. There are no pharmacologic therapies approved by the Food and Drug Administration available to treat restenosis at present. Brachytherapy, gamma or beta, is an effective adjunctive therapy that can reduce recurrent in-stent restenosis by 40% to 70%. Patients at high risk for recurrent in-stent restenosis (proliferative or total occlusion pattern) can be considered for brachytherapy to treat the first episode of in-stent restenosis. Patients with focal in-stent restenosis should be treated with brachytherapy after multiple recurrences of in-stent restenosis. Emerging therapies for treatment of restenosis include antiproliferative-coated stents and photoangioplasty.

Recombinant soluble p-selectin glycoprotein ligand-1-Ig reduces restenosis through inhibition of platelet-neutrophil adhesion after double angioplasty in swine

BACKGROUND

P-selectin mediates leukocyte recruitment to activated platelets and endothelium through its high-affinity receptor P-selectin glycoprotein ligand-1 (PSGL-1). Platelet and leukocyte activation and binding have been reported after coronary angioplasty and were correlated with restenosis. We investigated the effect of a recombinant soluble PSGL-1 (rPSGL-Ig) on the adhesion of platelets and neutrophils and the development of restenosis after double arterial injury.

METHODS AND RESULTS

Four weeks after angioplasty of both carotid arteries in pigs, a second angioplasty was performed at the same sites, 15 minutes after a single administration of vehicle or rPSGL-1 (1 mg/kg IV). Animals were euthanized 1 hour, 4 hours, 1 week, or 4 weeks later. Adhesion of autologous (51)Cr-platelets and (111)In-neutrophils was quantified and histological/morphometric analyses were performed. Although rPSGL-Ig did not affect adherence of these cells 1 hour after injury, it significantly reduced the adhesion of platelets (50% at 4 hours and 85% at 1 week) and neutrophils (50% at 4 hours and 78% at 1 week) to deeply injured arteries. At 4 weeks, the residual lumen was 63% larger in rPSGL-Ig-treated arteries as compared with control arteries (6.1+/-0.6 versus 3.8+/-0.1 mm(2); P:<0.002). The neointimal area was slightly reduced (0.5 in rPSGL-Ig versus 0.7 mm(2) in control). The ratio of the external elastic lamina of injured to uninjured reference segments was >1 in treated arteries and <1 in control arteries.

CONCLUSIONS

P-selectin antagonism with rPSGL-Ig inhibits early platelet/leukocyte adhesion on injured arteries and reduces restenosis through a positive impact on vascular remodeling. Hence, rPSGL-Ig may have potential in the prevention of restenosis.

Mechanisms involved in the inhibition of neointimal hyperplasia by abciximab in a rat model of balloon angioplasty

Monoclonal antibodies raised against beta(3) integrin are able to inhibit the binding of ligands to certain beta(3) integrins such as alpha(IIb)beta(3) (glycoprotein IIb/IIIa complex) and alpha(v)beta(3) (vitronectin receptor) and as such are inhibitors of platelet aggregation and smooth muscle cell (SMC) migration, both of which are involved in neointimal hyperplasia. The present study was designed to explore the detailed mechanisms of abciximab (Reopro), a monoclonal antibody (mAb) raised against alpha(IIb)beta(3) integrin in neointimal hyperplasia. In this study, carotid arteries of Wistar rats were damaged, and neointimal hyperplasia and lumen occlusion was determined at different time points. Abciximab was administered intravenously by an implanted osmotic pump. Abciximab (0.25 mg/kg/day) time-dependently inhibited both neointimal hyperplasia and lumen occlusion after angioplasty in carotid arteries of rats. Furthermore, the electromicrographs highlighted that SMCs were phenotypically different from the typical contractile, spindle-shaped SMCs normally seen in uninjured vessel walls. Platelet-derived growth factor (PDGF)-BB was strongly produced in thrombus formation and neointimal SMCs after angioplasty, while abciximab significantly reduced PDGF-BB expression in vessel lumens and neointimal SMCs after angioplasty. Balloon angioplasty caused a significant increase of nitrate and cyclic GMP as compared with sham-operated rats. Infusion of abciximab (0.25 mg/kg/day) did not significantly change. Furthermore, the plasma level of thromboxane B(2) (TxB(2)) obviously increased after angioplasty, while abciximab markedly suppressed the elevation of plasma TxB(2) concentration. The results indicate that abciximab effectively prevents neointimal hyperplasia, possibly through the following 2 mechanisms: (1) Abciximab binds to alpha(IIb)beta(3) integrin on platelet membranes resulting in inhibition of platelet adhesion, secretion, and aggregation in injured arteries, followed by inhibition of thromboxane A(2) formation and PDGF-BB release from platelets. (2) Abciximab may also bind to alpha(v)beta(3) integrin on SMCs, thus, subsequently inhibiting cell migration and proliferation.

Mechanical behaviour modelling of balloon-expandable stents

Endoprostheses are small struts placed by intravascular way to restore the vascular lumen and flow conditions. The purpose of this work is to provide models for evaluation and characterisation of some mechanical properties of a balloon-expandable stent by using the finite element method. Here we present the results for a metallic tubular peripheral prosthesis: the P308 Palmaz stent. We focus on the mechanisms linked to the structure expansion and its long-term behaviour. Several models are constructed in order to determine the stent shape after dilation and to assess the stress and strain fields in its wall due to this transformation. They inform us about the shortening percentage on expansion, degrees of radial and longitudinal recoil, and weaknesses of the structure. Various methods, differing in their levels of complexity, are then attempted to exhibit the predominant factors responsible for the crushing of a stent under external pressure. Moreover, the sensitivity of this critical pressure to geometric imperfections is studied. Lastly, since this kind of material is implanted for a lifetime, we test the stent with regard to fatigue life. Beyond safety considerations, this type of characterisation provides mechanical properties that are often difficult to obtain by experiments. If it was available for various stents, such information could be used to choose the appropriate prosthesis for specific applications. Moreover, confronted with observations from practitioners, they might lead to a better understanding of the failure or success of a particular design and to work on the product optimisation.

Minoxidil inhibits proliferation and migration of cultured vascular smooth muscle cells and neointimal formation after balloon catheter injury

The goal of the study was to investigate the in vitro and in vivo inhibition of minoxidil on smooth muscle cell (SMC) proliferation and migration as well as neointimal formation. The in vitro effect of minoxidil was investigated by Boyden chamber assay and cell-cycle analysis. To evaluate the in vivo effect, we treated the animals with minoxidil in their drinking water before and after balloon catheter injury to carotid artery. Results showed that minoxidil inhibited SMC migration across type I collagen membrane in a dose-related manner (13.5% by 0.01 mg/ml; p < 0.05; 16.8% by 0.05 mg/ml: p < 0.01; 40.4% by 0.25 mg/ml; p < 0.001; and 65.8% by 1.25 mg/ml; p < 0.001). Minoxidil (0.8 mg/ml) increased the number of SMCs in G1 phase (p < 0.05) and decreased the number of SMCs in S phase (p < 0.001). In vivo minoxidil treatment reduced neointimal mass by 31.7% (120 mg/L) and 42.3% (200 mg/L), respectively. Data demonstrate that minoxidil inhibits vascular SMC proliferation and migration both in vitro and in vivo, and therefore may be useful to inhibit SMC hyperplasia that occurs in restenosis and other vascular diseases.

Optimally deployed stents in the treatment of restenotic versus de novo lesions

Results from earlier trials performed before the implementation of optimal stent deployment techniques suggest that stenting for restenotic lesions may be associated with a higher risk of restenosis when compared with de novo lesions. The aim of this study was to compare the short- and long-term outcome of optimal stent deployment in restenotic versus de novo lesions. In all, 1,865 consecutive patients with 2,707 de novo lesions and 489 patients with 633 restenotic lesions underwent intravascular ultrasound-guided optimal stent deployment. In-hospital outcome was similar for both groups, except for a higher incidence of non-Q-wave myocardial infarction in the de novo group (14.6% vs 8.6%, p = 0.001). At 12-month follow-up, there was no statistical significant difference in the incidence of death or myocardial infarction, but event-free survival was better in the de novo lesion group of patients (74.5% vs 63.7%, p = 0.001). There was a higher incidence of target lesion revascularization in the restenosis group (25.1% vs 13.0%, p = 0.001). By multivariate analysis, restenotic lesions, vein graft lesions, and diabetes mellitus were strong determinants of repeat revascularization, whereas larger preprocedural reference vessel minimal lumen diameter and larger final minimal lumen diameter were associated with a reduced chance of restenosis and increased event-free survival. This study shows that optimal stent deployment for restenotic and de novo lesions has favorable short- and long-term outcome. However, the incidence of target lesion revascularization was significantly greater in restenotic lesions. Saphenous vein graft lesions and diabetes mellitus were confirmed as other independent risk factors for clinical restenosis.

Design and dosimetry of a novel 90Y beta source to prevent restenosis after angioplasty

PURPOSE

Post-dilatation irradiation of the vessel wall is currently under investigation for prevention of restenosis after balloon dilatation. For the irradiation, special sources were designed for animal experiments which would give equivalent irradiation conditions and doses to the vessel wall that would later be employed for human application.

METHODS AND MATERIALS

For the planned irradiations, a specially designed yttrium-wire of 0.45-mm diameter coated with a thin shrink tube to prevent contamination was deployed. Several leakage tests applied before and after application proved that the irradiation source was leakproof. Dosimetry was performed by using 0.1-mm-thick thermoluminescent dosimeters (TLD-100) calibrated against a primary standard. A shielding transport and application container was designed to facilitate the handling of the source during use, while reducing exposure of the medical personnel.

RESULTS

The designed source proves to be flexible for the insertion into proximal coronary vessels, and positioning at the site of stenosis. It provides an optimum protection of the animal and requires little radiation protection efforts on behalf of the medical staff. Dosimetric calculations and measurements showed that a centering of the source inside the vessel could be achieved with a maximum deviation of 50% between maximum and average dose levels.

CONCLUSION

A yttrium-90 beta brachytherapy source was designed which provides high flexibility within proximal coronary arteries, ensures an adequate centering inside the artery, and provides irradiation conditions to the vessel wall of the experimental animal comparable to the application inside a human artery.

Pharmacogenetic analysis of the effect of angiotensin-converting enzyme inhibitor on restenosis after percutaneous transluminal coronary angioplasty

Angiotensin-converting enzyme (ACE) inhibitors are reported to prevent neointimal formation after balloon injury in animal models, but in most prospective studies in humans, ACE inhibitors failed to prevent restenosis after percutaneous transluminal coronary angioplasty (PTCA). The ACE genotype assigned by an insertion/deletion (I/D) polymorphism is known to affect the potency of ACE inhibitors in several renal diseases. The authors attempted to clarify whether the effect of ACE inhibitors on restenosis might be modified by the ACE genotype. A total of 126 patients was randomly and prospectively assigned to the control group and the imidapril group. In the imidapril group, patients received 5 mg imidapril daily, starting 1 day before PTCA and continuing for 3 to 6 months. Forty-six control (65 vessels) and 32 imidapril patients (43 vessels) completed the study. The minimal lumen diameter before and after the procedure did not differ significantly among the groups with the three genotypes (II, ID, and DD) in both the control and imidapril groups. Late luminal loss during the follow-up period was not related to the ACE genotype in the control group but was significantly related in the imidapril group (II, 0.63+/- 0.19 mm; ID + DD, 1.12+/-0.14 mm, p<0.05). Furthermore, in the II genotype, imidapril significantly reduced late loss and restenosis rate as defined by most of the frequently used definitions. In conclusion the ACE I/D polymorphism may influence the effect of ACE inhibitors in preventing restenosis after PTCA.

In vitro cytotoxicity and in vivo biocompatibility of poly(propylene fumarate-co-ethylene glycol) hydrogels

The in vitro cytotoxicity and in vivo biocompatibility of poly(propylene fumarate-co-ethylene glycol) [P(PF-co-EG)] hydrogels were assessed in order to investigate the influence of poly(ethylene glycol) molecular weight and copolymer composition. These materials have application as injectable cardiovascular implants; cytotoxicity due to leachable products, as well as inflammation caused by the biomaterial itself, may ultimately affect the biocompatibility of the implant. We utilized a 7-day in vitro cytotoxicity assay to quantify cell density and cellular proliferation in the presence of copolymer films. The copolymer films exhibited slight to moderate cytotoxicity toward cultured endothelial cells, showing 20-86% viability relative to controls. Cell viability increased with an increasing weight percent of PEG or, to a lesser extent, the molecular weight of PEG. In vivo biocompatibility was assessed using a cage implantation model over a 21-day time period. This system was used to characterize the local cellular and humoral inflammatory response in the surrounding exudate, as well as the size and density of macrophages adherent to the material itself. All copolymer formulations exhibited excellent biocompatibility relative to controls with no significant differences in total leukocyte count among the different formulations. The in vivo inflammatory reaction displayed normal wound healing over 21 days as shown by a progressive decrease in both leukocyte concentration and enzymatic activity. The surface coverage of the copolymer films remained relatively constant from 7 to 21 days. There were no cells larger than 0.003 mm2, which was previously shown to be the threshold value for foreign-body giant cells. These data suggest that P(PF-co-EG) hydrogels have potential for use as injectable biomaterials.

Development of poly(propylene fumarate-co-ethylene glycol) as an injectable carrier for endothelial cells

Poly(propylene fumarate-co-ethylene glycol) [P(PF-co-EG)] hydrogels were examined as in situ polymerizable carriers for endothelial cells. The temperature increase from 37 degrees C during cross-linking was measured. The maximum temperature did not increase above 38.3 degrees C for any copolymer formulation. The temperature profiles also appeared to be independent of the amount or molecular weight of poly(ethylene glycol). These materials were polymerized in situ in a subcutaneous rat model and evaluated for initial biocompatibility. A normal wound-healing response was seen with formation and subsequent maturity of a fibrous capsule. Endothelial cells were embedded in vitro during the cross-linking process and their proliferation was assessed over the first 24 h. There was significant DNA synthesis by the embedded endothelial cells during this time period. These data suggest that P(PF-co-EG) hydrogels could be developed for use as injectable cell carriers.

The prevalence of Chlamydia pneumoniae in atherosclerotic and nonatherosclerotic blood vessels of patients attending for redo and first time coronary artery bypass graft surgery

OBJECTIVES

To determine if Chlamydia pneumoniae (C. pneumoniae) is more prevalent in atherosclerotic compared with normal blood vessels of patients requiring redo and first time coronary artery bypass graft surgery (CABG).

BACKGROUND

Serological and pathological studies have associated atherosclerosis with C. pneumoniae infection. As atherosclerosis is one of the causes of graft failure following CABG, then it may be expected that the prevalence of the organism in failed grafts and diseased native vessels should be greater than in the new grafts.

METHODS

Endarterectomy specimens and failed and new grafts were collected from 49 patients with late graft failure. Endarterectomy specimens and new grafts were also collected from nine patients having first time CABG. The presence of C. pneumoniae DNA was then checked for using a nested polymerase chain reaction.

RESULTS

The prevalence of C. pneumoniae DNA in failed venous grafts (38.2%) was similar to that in endarterectomy specimens from native coronary arteries (38.5%) and greater than that in new saphenous vein grafts (11.8%). However, it was similar to that in new internal mammary artery grafts (30.0%). Also, the interval between surgery in redo patients was the same regardless of whether C. pneumoniae was present or not.

CONCLUSIONS

Cross sectional studies cannot determine whether C. pneumoniae is a cause of atherosclerosis since they do not show whether infection precedes or follows its development. However, our results suggest that the organism is not an important factor in graft failure or atherosclerosis.

In vitro and in vivo degradation of poly(propylene fumarate-co-ethylene glycol) hydrogels

The degradation of poly(propylene fumarate-co-ethylene glycol) hydrogels was examined in vitro in phosphate-buffered saline at pH 7.4 and in vivo in a subcutaneous rat model. These hydrogels have potential application as biodegradable, injectable cardiovascular stents, and, as such, their mass loss, dimensional changes, mechanical properties, morphology, and biocompatibility over a 12-week time course were evaluated. Three formulations were fabricated: one base formulation consisting of 25% (w/w) PEG, molecular weight 4,600; one high weight percent PEG formulation with 50% (w/w) PEG; and one high molecular weight PEG formulation, molecular weight 10,500. All three formulations showed significant weight loss (between 40 and 60%) on the first day due to leaching of the uncrosslinked fraction. Further weight loss was observed only for the low weight percent PEG copolymers in the in vivo case, and a slight increase in volume was observed due to degradative swelling. The mechanical properties of the P(PF-co-EG) hydrogels decreased significantly in the first 3 weeks, showing the biphasic pattern typical of bulk degradation. In vitro, the hydrogels showed at least a 20% retention of their initial ultimate tensile stress after 3 weeks. The dynamic mechanical properties showed similar retention, with the in vivo mechanical properties differing from the in vitro properties only after 6 weeks of degradation. Differences in PEG molecular weight appeared to have little effect, but increasing the weight percent PEG decreased the rate of degradation both in vitro and in vivo. The morphology of the copolymer films, based on scanning electron microscopy observation, was not significantly different either among the three formulations or over the time course of the study, suggesting there were no macroscopic structural changes during this time period. The P(PF-co-EG) hydrogels demonstrated good initial biocompatibility, showing responses characteristic of biomaterial implants.

Preparation and characterization of poly(propylene fumarate-co-ethylene glycol) hydrogels

We describe the preparation and bulk characterization of a cross-linked poly(propylene fumarate-co-ethylene glycol), p(PF-co-EG), hydrogel. Eight block copolymer formulations were made varying four different design parameters including: poly(ethylene glycol) (PEG) molecular weight, poly(propylene fumarate) (PPF) molecular weight, copolymer molecular weight, and ratio of PEG to PPF. Two different cross-linking formulations were also tested, one with a cross-linking monomer and one without. The extent of the cross-linking reaction and the degree of swelling in aqueous solution were determined on copolymer formulations made without a cross-linking monomer. The values of molecular weight between cross-links, Mc ranged from 300 +/- 120 to 1190 +/- 320 as determined from swelling data (n = 3). The equilibrium volume swelling ratios, Q, varied from 1.5 +/- 0.1 to 3.0 +/- 0.1. This ratio was found to increase with increasing PEG content in the copolymer and decrease with increasing PPF molecular weight. The values for complex dynamic elastic moduli magnitudes of E*, ranged from 0.9 +/- 0.2 to 13.1 +/- 1.1 MPa for the formulations with the cross-linking monomer, N-vinyl pyrrolidinone (VP) (n = 3). The ultimate tensile stresses on the formulations made with VP ranged from 0.15 +/- 0.03 to 1.44 +/- 1.06 MPa, and tensile moduli ranged from 1.11 +/- 0.20 to 20.66 +/- 2.42 MPa (n = 5). All of the mechanical properties increased with increasing PPF molecular weight and decreased with increasing PEG content in the copolymer. These data show that the physical properties of p(PF-co-EG) hydrogels can be tailored for specific applications by altering the material composition.

Panic disorder in coronary artery disease patients with noncardiac chest pain

In this study we address the following questions: (1) What percentage of coronary artery disease (CAD) patients that present with chest pain, but whose symptoms cannot be fully explained by their cardiac status, suffer from panic disorder (PD)? (2) How do patients with both CAD and PD compare to patients without CAD and to patients without either PD or CAD in terms of psychological distress? Four hundred forty-one consecutive walk-in emergency department patients with chest pain underwent a structured psychiatric interview (ADIS-R) and completed psychological scales. Fifty-seven percent (250 of 441) of these patients were diagnosed as having noncardiac chest pain and constituted this study's sample. A total of 30% (74 of 250) of noncardiac chest pain patients had a documented history of CAD. Thirty-four percent (25 of 74) of CAD patients met criteria for PD. Patients with both PD and CAD displayed significantly more psychological distress than CAD patients without PD and patients with neither CAD nor PD. However, they did not differ from non-CAD patients with PD. PD is highly prevalent in patients with CAD that are discharged with noncardiac diagnoses. The psychological distress in these patients appears to be related to the panic syndrome and not to the presence of the cardiac condition.