Heparin adheres to the damaged arterial wall and inhibits its thrombogenicity

Polycaprolactone/gelatin degradable vascular grafts simulating endothelium functions modified by nitric oxide generation

Aim: Host remolding with scaffolds degradation and rapid formation of a complete endothelium, are prospective solutions for improving performance of small diameter vascular grafts. Materials & methods: For this purpose, microfibrous polycaprolactone (PCL)/gelatin scaffolds were prepared by electrospinning and subsequently functionalized with heparin and organoselenium-immobilized polyethyleneimine for nitric oxide generation through layer-by-layer self-assembly. Results: Our results showed that modified PCL/gelatin grafts had strong catalytic nitric oxide generation capacity and facilitated the enhanced attachment of endothelial cells, compared with control scaffold groups. Meanwhile, the modified grafts exhibited good hemocombatility, rapid endothelialization and smooth muscle cell regeneration. Conclusion: Modification of biodegradable scaffolds, proposed in this work, could enhance biological functions of vascular grafts and provides new strategies for the construction of small diameter vascular grafts.

Mechanism of antithrombotic effect of heparin and antithrombin in balloon-injured arteries

The mechanism of the antithrombotic effects of heparin and the synthetic antithrombin agent argatroban was evaluated in a dog model. Thrombus formation following balloon injury was evaluated by angioscopy in the right iliac arteries of 20 dogs to serve as a control. After the evaluation of the growth of thrombus on the control side, heparin (200 U/kg) or argatroban (0.2 mg/kg) was infused intravenously, and the distal site of the contralateral left iliac artery was injured in the same manner. At 30 to 120 min before the final examination, the proximal site of the left iliac artery also was injured. After antithrombotic drug infusion, the percent angioscopic stenosis at the distal site was much lower (P<0.0001) than that of the control site (mean stenosis index: 0.67 in heparin vs. 3.8 in control, and 0.25 in argatroban vs. 4.3 in control); however, thrombus formation was observed at the proximal site. With local delivery of a low dose of either antithrombotic drug (n=10), an antithrombotic effect was maintained until 4 h after the infusion. A very weak fluorescence of FITC-heparin was detected at the injured artery 2 h after infusion. In a shunt experiment involving 5 dogs, carotid arteries were injured and incubated in oxygenated Krebs--Henseleit solution before auto grafting into the femoral artery. At 2 h after the grafting, no thrombus was formed in the grafted vessels incubated for 4 h, but was formed in those incubated for 10 min. These results indicate that the relatively long antithrombotic effect of these drugs may be due to a local drug effect at the injured artery, as well as the recovery of the anti-thrombogenicity of the injured artery.

Cell-free xenogenic vascular grafts fixed with glutaraldehyde or genipin: in vitro and in vivo studies

Chronic rejection of arterial xenografts results in aneurysmal dilation, due to immune mediated processes. To minimize the immunologic degradation of the graft, a cell-extraction process employing sodium dodecyl sulfate (SDS) was used in the study to remove the cellular components in bovine carotid arteries. To further reduce their immunogenicity, the acellular arteries were fixed with glutaraldehyde (A-GA) or genipin (A-GP). The in vitro properties of all test samples were analyzed. Additionally, the in vivo performance of the heparinized A-GA and A-GP grafts (H-A-GA and H-A-GP) was evaluated in a canine model. It was found that the SDS treatment effectively removed cells from the arterial wall, but the main structures of the extracellular matrix were preserved with a portion of the water-soluble glycosaminoglycans removed. After cell extraction, the elastic lamellae in the media became straightened, and thus made the tissue less extensile. The heparinized tissues significantly reduced platelet adhesion. At retrieval, all implanted grafts were patent and not dilated. Chronic inflammatory response surrounding the implants was observed. However, fixation of acellular tissues by glutaraldehyde or genipin inhibited immune cell penetration into the media and limited tissue degradation, and therefore prevented the arterial wall from dilation. Nevertheless, the H-A-GP graft was superior to the H-A-GA graft in completeness of endothelialization on its luminal surface, and thus precluded thrombus formation.

Nitrosoglutathione modulation of platelet activation and nitric oxide synthase expression in promotion of flap survival after ischemia/reperfusion injury1

BACKGROUND

Recent studies have shown that platelets play an important role in the pathogenesis of reperfusion injury. Using an inferior epigastric artery skin flap as a flap ischemia/reperfusion (I/R) injury model, we investigated whether the administration of a nitric oxide (NO) donor, nitrosoglutathione (GSNO), could decrease platelet activation and modulate the NO synthase (NOS) activity of platelets and promote flap survival.

METHODS

Thirty minutes before flap reperfusion, normal saline (1 mL), nitrosoglutathione (GSNO 0.2, 0.6, 3 mg/kg), or N(G)-nitro-L-arginine-methyl ester (450 mg/kg) was injected intravenously in 10 rats, respectively. The p-selectin (CD62P) expression of platelet activation was detected by a flow cytometry. Immunohistochemical staining was performed to investigate the CD62P deposition on the microvasculature of the flap vessels. NOS isoform expression in the platelets was evaluated by Western blot. Tissue perfusion was monitored by using laser-Doppler flowmetry. Survival areas were assessed at 7 days postoperatively

RESULTS

An optimal dose of GSNO (0.6 mg/kg), significantly decreased in CD62P expression on platelets (P < 0.001) and its deposition on the flap vessels, selectively suppressed iNOS induction of platelet, and significantly improved blood perfusion and the flap survival rate (59.8 +/- 4.9% versus 22.1 +/- 6.1%, P < 0.001). In contrast, the NO synthase inhibitor, N(G)-nitro-l-arginine methyl ester, although inhibiting iNOS expression of platelets, compromised platelet activation, tissue perfusion, and flap survival.

CONCLUSION

This study suggests that GSNO can appropriately donate NO to suppress platelet activation and platelet iNOS induction, resulting in less platelet activation, better blood perfusion, and flap survival after I/R injury.

Nitrosoglutathione improves blood perfusion and flap survival by suppressing iNOS but protecting eNOS expression in the flap vessels after ischemia/reperfusion injury

BACKGROUND

The effects of nitric oxide (NO) on the microcirculation and free tissue survival remain controversial. With the use of a rat inferior epigastric artery flap as an ischemia/reperfusion injury (I/R) model, we investigated whether exogenous NO donation regulates endogenous NO synthase (NOS) expression in the flap vessels and promotes flap survival.

METHODS

Thirty minutes before flap reperfusion, normal saline (1 ml), nitrosoglutathione (GSNO 0.2, 0.6, 3 mg/kg), or N(G)-nitro-L-arginine-methyl ester (L-NAME, 450 mg/kg), was injected intravenously into 20 rats. Total plasma NOx (NO(2)-/NO(3)-) was measured to reflect NO production. Immunohistochemical staining was investigated for the endothelin-1 (ET-1) and NOS isoforms expression on the flap vessels. NOS isoforms expression was evaluated by Western blot. Laser-Doppler flowmetry monitored flap perfusion. Survival areas were assessed by gross examination at 7 days postoperatively.

RESULTS

Flap ischemia at 12 hours followed by reperfusion resulted in endothelial cell damage, as demonstrated by induction of iNOS and ET-1 expression in the flap vessels. An optimal dose of nitrosoglutathione (0.6 mg GSNO/kg) significantly increased plasma NOx levels (P=.027) and improved flap perfusion by laser Doppler measurement (P=.014), and increased the flap viability area (P<.001). Additionally, it selectively suppressed iNOS induction, but enhanced eNOS expression and decreased ET-1 deposition in the flap vessels. In contrast, an NOS inhibitor, N(G)-nitro-L-arginine methyl ester, inhibited both iNOS and eNOS expression in the flap vessels, decreased endogenous NOx production, and compromised flap viability.

CONCLUSION

This study indicates that intravenous administration of exogenous GSNO can appropriately donate NO to suppress iNOS induction and enhance eNOS expression in pedicle vessels, resulting in better blood perfusion and a higher flap survival after I/R injury.

Reactive thrombocytosis without endothelial damage does not affect the microvascular anastomotic patency

There is still controversy about the correlation of thrombocytosis and thrombosis complication. Using a rodent splenectomy-induced thrombocytosis model and a thrombogenic endothelial damage model (inverted suture resulting in an intraluminal thrombogenic adventitia of divided femoral artery), the authors investigated whether reactive thrombocytosis with or without endothelial damage contributes to the patency of microvascular anastomosis. Four experimental groups were evaluated in this study: 1) sham operation without thrombogenic anastomosis after femoral artery division; 2) sham operation with thrombogenic anastomosis; 3) thrombocytosis alone without thrombogenic anastomosis; 4) thrombocytosis with thrombogenic anastomosis (each subgroup n = 10, total N = 40). Vascular patency was assessed after immediate operation and on the seventh day postoperatively. Platelet counts and platelet activation (CD62P) were studied in correlation to microvascular patency. In rats without thrombogenic anastomosis groups, there were no significant differences in CD62P expression on platelets (p = 0.09), the patency rates (p = 0.561), or perfusion units (p = 0.746) before and after arterial reanastomosis between rats with and without thrombocytosis, respectively. However, the thrombogenic anastomosis of femoral artery in thrombocytosis and control groups showed significantly increased CD62P expression (p < 0.05), decreased the perfusion unit (p < 0.05), and patency rate (p < 0.001), compared with rats without thrombogenic anastomosis of femoral artery in both groups. In summary, this study demonstrates that microvascular anastomosis can be performed safely with reactive thrombocytosis alone without thrombogenic anastomosis. Meticulous microvascular anastomosis without triggering platelet activation is the most important factor to prevent thrombosed vessels in microsurgical anastomosis.

Platelet glycoprotein IIb/IIIa receptor antagonist (abciximab) inhibited platelet activation and promoted skin flap survival after ischemia/reperfusion injury

BACKGROUND

Evidence has shown that platelets play an important role in the pathogenesis of flap failure. Employing a rat inferior epigastric artery skin flap as a flap reperfusion injury model, we investigated whether platelet activation was involved in the skin flap failure and whether administration of abciximab (ReoPro, chimeric 7E3 Fab) could decrease platelet activation/aggregation and promote flap survival.

METHODS

Normal saline and abciximab (0.06 mg/kg; 0.2 mg/kg; 1 mg/kg) were injected intravenously into skin flaps 30 min before reperfusion and 1 h after reperfusion (each subgroup n = 6). Platelet activation as demonstrated by P-selectin (CD62P) was analyzed by flow cytometry. P-selectin expression on flap vessels was detected by immunohistochemical staining. Platelet aggregation was induced with adenosine diphosphate (ADP). Laser Doppler flowmetry monitored tissue perfusion. The surviving area was evaluated 7 days postoperatively.

RESULTS

CD62P progressively increased after reperfusion. The peak CD62P occurred after reperfusion for 12 h. Immunohistochemical staining showed CD62P significantly deposited on the endothelium after reperfusion. Administration of abciximab (1 mg/kg) effectively improved flap survival rate (P = 0.003), significantly decreased ADP-induced platelet aggregation (P < 0.001), and suppressed CD62P expression on blood platelets (P = 0.002) and its deposition on the flap vessels.

CONCLUSION

Abciximab promotion of skin flap survival is due to blocked platelet activation/aggregation and decreased activated-platelet deposition on the vascular endothelium. Thus, administration of a platelet glycoprotein IIb/IIIa receptor antagonist such as abciximab may save the skin flap from reperfusion injury after a long period of ischemia.

Reduction in neointimal formation with a stent coated with multiple layers of releasable heparin in porcine coronary arteries

Recent studies demonstrated that neointimal formation, which is caused by both neointimal proliferation and organized mural thrombus, is responsible for in-stent restenosis. Although various types of heparin coatings were effective in reducing (sub)acute thrombosis, most of them failed to reduce neointimal proliferation. This study was designed to examine the effect of the stent coated with multiple layers of releasable heparin complex from which heparin diffuses into the surrounding tissue and exerts its beneficial effects. Male Yorkshire pigs underwent balloon expandable stenting for coronary segments of both the left anterior and the left circumflex coronary arteries with a comparable diameter (n = 10). The stent implantation site was randomized for either control or heparin-coated stent. Four weeks after the procedure, quantitative coronary angiography (QCA) and intravascular ultrasonographic imaging (IVUS) were performed followed by histologic analysis. In additional animals, staining for proliferating cell nuclear antigen (PCNA) was performed 10 d after the procedure (n = 3). QCA demonstrated that coronary diameter (mm) was significantly larger at the heparin-coated stent site (2.32 +/- 0.14) compared with the control stent site (1.81 +/- 0.17) (p < 0.01). IVUS also showed that the neointimal area (mm2) was significantly suppressed at the heparin-coated stent site (2.12 +/- 0.58) compared with the control stent site (3.92 +/- 0.33) (p < 0.01). Histologic analysis also demonstrated that neointimal area (mm2) was significantly less at the heparin-coated stent (2.94 +/- 0.43) than at the control stent site (4.41 +/- 0.38) (p < 0.01), which was also the case for organized thrombus area (x10-4 mm2) (6.61 +/- 2.67 vs. 19.36 +/- 4.38, p < 0.01). The frequency of PCNA-positive vascular smooth muscle cells (%) was significantly less at the heparin-coated stent (10.8 +/- 1.0) than at the control stent site (19.1 +/- 1.7) (p < 0.01). These results suggest that the stent coated with releasable heparin is beneficial in reducing neointimal formation and subsequent in-stent restenosis.

Local antithrombotic therapy using a novel porous balloon catheter

The efficacy of local treatment of thrombosis with low-dose antithrombotic drugs (heparin: 30 U/kg, or argatroban: 0.02 mg/kg) was investigated using a novel porous balloon catheter. This novel balloon catheter can deliver drug into arterial walls without causing vascular trauma. Thrombus formation was significantly inhibited in balloon-injured and locally-treated iliac arteries compared with control balloon-injured arteries in 12 dogs. In the systemic high-dose delivery group (ten times as high as the low dose), thrombus formation in injured arteries was significantly less than that of controls in 7 dogs. Low-dose systemic delivery was not effective at inhibiting this thrombus formation. Thus, local treatment with an antithrombotic drug using this novel porous balloon catheter can prevent thrombosis without influencing systemic coagulability.

Sustained local delivery of heparin to the rabbit arterial wall with an electroporation catheter

Current methods of local drug delivery frequently fail to achieve a prolonged therapeutically effective tissue drug level without producing vascular trauma. A novel double-balloon catheter system, incorporating electroporation technology, has been designed and tested to deliver heparin into rabbit carotid arteries in an overstretch balloon injury model in vivo. Following arterial injury, fluoresceinated heparin was delivered into the volume between the two inflated balloons, and the artery was subjected to an electrical pulse. Catheter deployment and endovascular electrical pulsing were well-tolerated in all animals (N = 21) without adverse hemodynamic and histological changes. Periodic arterial blood samples revealed no abnormalities in the clotting profile or any gross morphological changes in the blood cells up to 8 hr after treatment. Much stronger heparin fluorescence was detected throughout the vessel layers for at least 12 hr in the pulsed samples compared to the control. Histochemical staining of the tissue showed intracellular localization of heparin. Endovascular electroporation may provide better retention and higher therapeutic efficacy than can be achieved by conventional systemic delivery of heparin at clinically safe concentrations.

Laser balloon angioplasty combined with local intracoronary heparin therapy: immediate and short-term follow-up results

Laser balloon angioplasty (LBA) has been shown to acutely increase angiographic luminal dimensions after conventional balloon angioplasty (PTCA) without a favorable impact on chronic restenosis. Experimentally, laser and thermal energy enhance binding of heparin to the injured arterial wall and to the thrombus. In view of the anticoagulant, antiproliferative, and antifibrotic activities of the drug, a pilot study was performed to evaluate the potential safety and efficacy of LBA combined with local heparin therapy. Ten patients scheduled for elective PTCA were entered in the study. In each patient, a single lesion was treated with a laser balloon and coated with a heparin film (3000 I.U. at a concentration > 100,000 I.U./gm) immediately after optimal PTCA. The mean minimum luminal diameter and mean percent stenosis of the 10 treated lesions after PTCA were 1.62 +/- 0.39 mm and 37% +/- 9%, respectively. After LBA and local heparin therapy, the mean minimal lumen diameter increased to 2.01 +/- 0.34 mm (p < 0.01) and the mean percent stenosis decreased to 20% +/- 10% (p < 0.01). Systemic heparin was discontinued immediately after the procedure in all patients. Acute or inhospital complications, either major or minor, occurred in none (0%) of the 10 patients (95% confidence interval 0% to 31%); all were discharged home on the day after the procedure. All patients remained well and free of cardiac symptoms for at least 2 months after the procedure. However, restenosis developed in six (60%) of the 10 patients (95% confidence interval 26% to 88%) 2 to 6 months after the procedure. The results suggest that LBA and local heparin therapy, with discontinuation of systemic heparin immediately after angioplasty, is a safe treatment modality that yields favorable acute angiographic results.

Local delivery of heparin to balloon angioplasty sites with a new angiotherapy catheter: pharmacokinetics and effect on platelet deposition in the porcine model

The purpose of this study was to assess the efficacy of local heparin delivery to balloon angioplasty sites in an in vivo porcine model by using a newly designed angiotherapy catheter that allows for prolonged drug infusion while maintaining distal arterial perfusion. Protocols were designed to assess the safety of intracoronary drug delivery, the effect of infusion time and drug concentration on intramural heparin deposition, the distribution of heparin within the arterial wall, the histologic effects of local heparin delivery, the wash-out of intramurally deposited heparin, and the effect of heparin delivery on early platelet deposition following balloon injury in peripheral and coronary vessels. Local intracoronary delivery of heparin was well tolerated in all animals. Between 0.04 and 0.08% of infused heparin was intramurally deposited at the time of drug delivery, with longer infusion durations and higher concentrations of heparin resulting in greater intramural deposition. Autoradiography demonstrated homogenous distribution of heparin throughout the intima, media, and adventitia, with localization in the nuclei, cytoplasm, and extracellular space. Histologic analysis demonstrated no additional vessel trauma from local drug delivery beyond that seen with conventional angioplasty. Wash-out studies demonstrated a biexponential disappearance of intramurally deposited drug, with rapid release of heparin over the first 60 min and persistence of small amounts of drug for at least 7 d. Locally delivered heparin significantly attenuated the deposition of platelets in peripheral vessels, although a similar decrease in platelet deposition in the coronary arteries was not statistically significant. Local delivery of heparin directly to coronary angioplasty sites is possible with the use of a new angiotherapy catheter. Wash-out of heparin from the arterial wall is initially rapid, although drug is detectable for up to 1 wk following delivery. In porcine peripheral arteries, use of this technique significantly decreases early platelet deposition following balloon injury.

Localized delivery of heparin to angioplasty sites with iontophoresis

Drug delivery by iontophoresis involves the application of an electric field to move selectively charged drug molecules across biological membranes. The purpose of this study was to assess the efficacy of intravascular iontophoresis in the local delivery of heparin to balloon angioplasty sites by using a recently designed iontophoretic catheter. In vivo heparin iontophoresis was assessed in 33 rats and 21 pigs in four protocols designed to measure the technical determinants of intramural drug deposition, the pharmacokinetics and localization of coronary delivery, and the effect of this technique on platelet deposition following balloon injury. First, iontophoresis of 3H-heparin into the aorta of 33 rats was performed to determine the effects of iontophoretic current, iontophoretic membrane balloon initiation pressure, iontophoresis time, and heparin concentration on intramural drug deposition. Second, iontophoresis of 3H-heparin was performed in 16 porcine coronary arteries to quantitate immediate drug delivery and subsequent wash-out over 24 h. Third, iontophoresis of fluorescent heparin was performed in 8 porcine coronary arteries to define intramural localization of locally delivered drug. Fourth, 111In-labeled platelet deposition was measured 1 h following balloon angioplasty and local iontophoretic heparin delivery in 16 porcine carotid and iliac vessels. Contralateral control vessels that were dilated with the same size balloon and treated with iontophoresis of saline served as controls. Rat aortic studies demonstrated that iontophoresis resulted in 13 times more intramural heparin deposition than passive delivery (passive: 0.3 +/- 0.4 microgram, iontophoresis: 4.6 +/- 1.6 micrograms, P < 0.0004). Iontophoretic membrane balloon inflation pressure had no significant effect on intramural drug deposition, but longer iontophoresis times and higher heparin concentrations resulted in higher levels of intramural heparin (P < 0.05). Porcine coronary studies demonstrated successful intramural deposition of heparin in all arteries without adverse electrical or hemodynamic sequelae, with persistence of the drug for at least 24 h. Localization studies demonstrated immediate deposition of fluorescent heparin in the intima and internal elastic lamina, with subsequent rapid diffusion of the drug into the media. Porcine platelet studies demonstrated that heparin iontophoresis decreased platelet deposition following balloon injury by approximately 66% compared with saline-treated control vessels (heparin-treated: 1.46 +/- 2.51 x 10(8), control: 4.27 +/- 7.02 x 10(8), P = 0.001). This study has demonstrated that local intramural heparin delivery is feasible with an intravascular iontophoretic catheter. Following intracoronary heparin iontophoresis in the porcine model, intramural drug is detected for at least 24 h. Local delivery of heparin with this technique significantly decreases early platelet deposition following balloon injury in peripheral porcine arteries.

Intramural drug delivery by direct injection within the arterial wall: first clinical experience with a novel intracoronary delivery-infiltrator system

Local drug delivery at the lesion site in patients with coronary artery disease is being intensively studied to prevent restenosis after percutaneous coronary intervention. However, the effective penetration of the delivered agents into the vessel wall and delivery time remain considerable problems for all currently existing devices. A unique, new catheter has been invented, the infiltrator Angioplasty Balloon Catheter (IABC), which has the capability to allow intramural drug delivery by direct injection within the arterial wall. We describe the first clinical experience with this catheter. IABC is an angioplasty catheter with 3 lumens: one for inflating the balloon, one central for the guidewire, and a third for drug delivery. On the surface of the balloon there are 3 longitudinal strips of 6 injection needles, which on inflation stand 0.01" high, and are connected to the drug-delivery lumen. With inflation of the balloon, the needles penetrate the lesion, allowing drug delivery into the media of the vessel wall. We used the IABC in 17 patients (age = 58 +/- 9 years) undergoing coronary angioplasty. All patients were symptomatic, with significant lesions (13 LAD, 3 LCX, 1 RCA) and documented ischemia. Following initial dilatation with a conventional angioplasty balloon (stenosis from 72 +/- 8% to 26 +/- 14%, P < 0.001), the IABC was used to infiltrate the lesion with 0.4 ml (6,000 IU) of low-molecular-weight heparin (Fraxiparine). For the delivery, the IABC was inflated to 1-2 atm for 30-45 s, and the heparin was injected by hand in 5 s. Lesion residual stenosis and morphology remained unchanged after IABC use (26 +/- 14% to 22 +/- 11%, P = NS). In 10 patients, stent placement followed the IABC use. The decision to proceed with stent placement was made after the initial dilatation with the conventional balloon, and it was not influenced by the IABC use. Stent placement greatly improved the final result (for the whole patient group: 22 +/- 11% to 5 +/- 18%, for the stented patients: 22 +/- 13% to -7 +/- 10%, P < 0.001 for both). Hospital course was uneventful, with no electrocardiogram changes and normal cardiac enzymes for all patients. We have shown that the use of a unique new catheter (IABC) for intramural drug delivery in human patients undergoing coronary angioplasty is feasible and safe. This catheter is the first of a new generation of catheters and represents a significant step in local drug delivery. It is very promising as a vehicle to modify plaque behavior and potentially influence restenosis after angioplasty.

Prolonged arterial occlusion caused by thrombus development at sites of arterial bifurcation

Although thrombogenic atheromas frequently develop at sites of arterial branching or bifurcation, the nature of such thrombus formation remains unclear. In this study, small rat mesenteric arteries (about 0.3 mm id) were observed using a video-microscope system. Exposure of the media by inducing compression damage over a short segment caused occlusive thrombus formation and subsequent spontaneous reperfusion repeatedly over about 30 min. Compression damage was induced either at a site just distal to the bifurcation (group 1, n = 7) or 5-10 mm downstream from the bifurcation (group 2, n = 7). The number of thrombotic occlusions was similar in the 2 groups, but the total duration of occlusion was significantly higher in group 1 (540 +/- 47 sec) than in group 2 (295 +/- 24 sec) (p < 0.01). The total duration of occlusion in group 1 was significantly reduced to 273 +/- 16 sec (p < 0.01) by mechanical interruption of flow in the other, intact, arterial branch. In the presence of blood flow through the intact branch, the occlusive thrombus at the bifurcation further enlarged in the direction of the intact branch, resulting in a significantly larger thrombus than in the absence of blood flow (17.1 +/- 2.1 vs 9.2 +/- 0.9 x 10(-2) mm2, p < 0.01). Stasis of the arterial blood per se did not affect the duration of thrombotic occlusion or increase plasma fibrinolytic activity. Thus, arterial occlusion caused by a thrombus arising at arterial bifurcations may be prolonged because of enlargement of the thrombus owing to the action of platelets in blood flowing through the intact branch.

Local delivery of antithrombotic drug prevents restenosis after balloon angioplasty in atherosclerotic rabbit artery

We investigated the ability of various antithrombotic drugs, delivered locally, to prevent restenosis after angioplasty in hypercholesterolemic rabbits. After dilating atherosclerotic iliac stenoses by balloon angioplasty, a low dose of heparin or a new antithrombotic drug, such as low molecular weight heparin (fragmin), argatroban, or batroxobin, was delivered locally using the balloon double-occlusion technique. In 1 group, high-dose heparin was administered intravenously. Animals that received no drugs served as a control group. After angioplasty, the stenotic segment was dilated and the mean percentage luminal stenosis fell from 89% to 9% in the group that received locally delivered heparin, from 88% to 7% in the group that received locally delivered argatroban, from 87% to 11% in the group that received locally delivered fragmin, from 88% to 15% in the group that received locally delivered batroxobin, from 82% to 18% in the group that received i.v. heparin (p < 0.0001 compared with before angioplasty in each case), and from 84% to 17% in the control group (p < 0.005 compared with before angioplasty). Twenty-eight days after angioplasty, the percentage luminal stenosis remained at 14% in the group that received locally delivered argatroban, 15% in the group that received locally delivered fragmin, and 28% in the group that received locally delivered batroxobin, whereas it increased to 45% in the group that received i.v. heparin, 30% in the group that received locally delivered heparin and 72% in the control group (p < 0.05 compared with after angioplasty in each case). Thus, local delivery low doses of new antithrombotic drugs prevents restenosis after angioplasty without affecting systemic coagulability; heparin, whether administered locally or intravenously, was less effective than the new drugs in preventing restenosis.

Effects of a single heparin bolus on neointimal growth after arterial injury in intact rabbits

Heparinization is a routine procedure during angioplasty; however, its consequences on the late vascular response to a severe injury are unclear. The authors' objective was to explore the effect of a single heparin bolus at the time of a severe vascular injury on late intimal proliferation and neointimal thickening. The iliac artery of 57 normolipemic rabbits was overdistended with a balloon catheter. Heparin (250 IU/kg i.v.) was given to 29 rabbits ten minutes before angioplasty, whereas 28 rabbits served as untreated controls. Neointimal thickening was prominent at fourteen days after injury and reached near-maximal values at day 28. The intimal/medial area ratio was reduced by an average 28.3% with heparin (at day 28: 2.19 +/- 0.51 vs 1.57 +/- 0.59, control vs heparin, P = 0.02). Neointimal cells stained positively for HHF-35 antibody, directed against smooth muscle cell antigens. Neointimal proliferation, quantified through the number of cell nuclei peroxidase-stained for PCNA/cyclin antigen, was significantly decreased by 43% and 49% with heparin, respectively, at days 7 and 14 after injury. These data suggest that early exposure even to low doses of heparin accounts for much of its inhibitory effect in vascular response to injury; such an effect might prove important in interpreting results of human trials of interventions against restenosis.

Local treatment with an antithrombotic drug reduces thrombus size in coronary and peripheral thrombosed arteries

Since the treatment of thrombotic disease by antithrombotic drugs may be associated with bleeding complications, a local delivery technique for administration of the drug may be useful. The efficacy of low-dose local delivery of an antithrombotic drug on thrombosis was investigated in 73 dogs. The antithrombotic drug (heparin, 25 U/kg, antithrombin: argatroban, 0.05 mg/kg, or defibrinogenating agent: batroxobin, 0.05 U/kg) was infused locally to a 1-h-old thrombus, and no drug was given in controls. The effect of the local delivery on the thrombus was evaluated. Low- and high-dose systemic drug delivery was also evaluated. The mean reduction in thrombotic coronary stenosis observed by angiography was 30.3% with argatroban, 22% with heparin, and 20.8% with batroxobin (P < 0.005 vs controls). Systemic delivery of low-dose heparin or argatroban did not induce any change in thrombus size. With high-dose systemic drug delivery (heparin 250 U/kg, argatroban 0.5 mg/kg), the mean reduction of thrombotic stenosis was 15.2% with heparin and 32.8% with argatroban (P < 0.005 vs controls). In the iliac arterial thrombosis, after local delivery of the drugs, the mean reduction of thrombotic stenosis observed by angiography was 24.4% in the argatroban group, and 19.2% in the heparin group (P < 0.05 vs controls, respectively). With high-dose systemic heparin delivery, the mean reduction of the thrombotic stenosis was 13.2% (P < 0.01 vs control). Angioscopy also demonstrated a similar trend. The high-dose drug delivery reduced systemic coagulability. Thus, local delivery of an antithrombotic agent can reduce the thrombus size in the coronary and iliac arteries without having any significant influence on coagulability.

Induction of thrombolysis and prevention of thrombus formation by local drug delivery with a double-occlusion balloon catheter

The efficacy of the local delivery of an antithrombotic drug in preventing thrombosis and enabling thrombolysis was investigated in 29 dogs. An antithrombotic drug (heparin, 25 U/kg), or an antithrombin (argatroban, 0.05 mg/kg) was infused into injured canine iliac arteries, using a double-occlusion balloon catheter, and the preventive effect of the drug was evaluated. Local delivery of low-dose tissue-type plasminogen activator (t-PA; Tisokinase, 50,000 U; Kowa, Nagoya and Asahi Chemical Industries, Fuji, Japan) into thrombosed canine iliac arteries, using the same catheter, or intravenous infusion of low-dose or high-dose t-PA (30,000 U/kg) was also performed. Angiographically, stenotic thrombosis was 2% by local delivery of argatroban and 7% by local delivery of heparin (P < 0.01 vs each control; 47% and 51% respectively). Thrombotic stenosis, as observed by angiography, decreased from 91% to 9% after local delivery of t-PA, and from 94% to 52% in controls. Local delivery of t-PA effectively reduced the thrombus size (P < 0.01 vs control). After systemic intravenous delivery of low-dose t-PA, no reduction of residual thrombotic stenosis, was observed. Reduction of residual thrombotic stenosis after intravenous delivery of high-dose t-PA, was similar to that achieved by local delivery of the drug. Angioscopy demonstrated a similar trend. High-dose drug delivery reduced systemic coagulability. Local delivery of an antithrombotic drug, using a double-occlusion balloon catheter, effectively prevented thrombus formation, and local delivery of t-PA induced thrombolysis without exerting a significant influence on coagulability.

Chronobiological aspects of pulmonary thromboembolism

A growing body of evidence has recently accumulated suggesting that several unfavorable cardiovascular events, e.g., myocardial angina and infarction, sudden cardiac death, and stroke, present a specific temporal pattern in their occurrence. This has also been shown to be true for fatal pulmonary thromboembolism, with a high frequence peak in winter and in the morning hours. The authors report the circannual and circadian aspects of pulmonary thromboembolism, analysing both the temporal patterns of the underlying favouring or precipitating factors, and the possible therapeutic implications.

Local treatment with antithrombotic drugs can prevent thrombus formation: an angioscopic and angiographic study

OBJECTIVES

This study was designed to evaluate the efficacy of local versus systemic treatment of thrombosis with various antithrombotic drugs.

BACKGROUND

Local use of low dose antithrombotic drugs has been proposed as being effective and safe.

METHODS

Heparin (30 U/kg), an antithrombin agent (argatroban, 0.05 mg/kg body weight) or a defibrinogenating drug (batroxobin, 0.05 U/kg) was locally infused into one side of the canine iliac artery after injury by balloon inflation. The other side was injured as a control. The efficacy of systemic delivery of high dose (heparin [300 U/kg] and argatroban [0.5 mg/kg]) and low dose drugs was also assessed.

RESULTS

Sixty minutes after local treatment in 22 dogs, no thrombotic stenosis was observed by angiography in locally treated arteries (p < 0.005 vs. mean thrombotic stenosis of 27% in control segments for heparin, 25.3% in control segments for argatroban and 32% in control segments for batroxobin). Angioscopy demonstrated the same trend. In locally treated arteries, thrombus weight was significantly lower in the treated than control side. In the systemic high dose group (n = 10), angiographic thrombotic stenosis was < 5% after high dose drug delivery (p < 0.05 vs. control segments, 37.4% for heparin, 43% for argatroban). In another 10 dogs, low dose systemic delivery was not effective in inhibiting thrombus formation. Activated partial thromboplastin time and fibrinogen levels did not change with local treatment.

CONCLUSIONS

Compared with systemic administration of antithrombotic drugs, local treatment is a safer and more effective method of preventing thrombosis.

Localized intramural drug delivery during balloon angioplasty using hydrogel-coated balloons and pressure-augmented diffusion

OBJECTIVES

This study was designed to assess the feasibility of using hydrogel-coated balloons to deliver biologically active agents to the blood vessel wall.

BACKGROUND

The local intramural delivery of therapeutic agents during balloon angioplasty has been proposed as an adjunctive technique for preventing early intracoronary thrombosis and late restenosis.

METHODS

To assess the efficacy of delivery and depth of penetration in vitro, local delivery of horseradish peroxidase was performed in 40 porcine peripheral arteries, and delivery of fluoresceinated heparin was performed in 20 porcine peripheral arteries and 7 human atheromatous arteries. To determine the persistence of these agents in the vessel wall in vivo, horseradish peroxidase was delivered to 18 porcine peripheral arteries that were harvested at intervals of 45 min to 48 h. Fluoresceinated heparin was delivered to 22 porcine peripheral arteries, 14 with the use of a protective sleeve, harvested at intervals of 30 s to 24 h.

RESULTS

In vitro agent delivery was successful in all specimens. The depth of penetration of horseradish peroxidase was directly related to both balloon pressure (p < 0.04) and duration of inflation (p < 0.01). In vivo peroxidase staining was evident at 45 and 90 min but not thereafter. With the use of a protective sleeve, heparin was present in all arteries harvested at 30 s, with marked dissipation at 1 and 24 h. Without a sleeve, no fluorescein staining was detected in any artery. With both agents, delivery occurred consistently over broad regions of the vessel wall that were free of architectural disruption.

CONCLUSIONS

Hydrogel-coated balloons can deliver biologically active agents to the vessel wall without gross tissue disruption and may provide an atraumatic method for the local delivery of therapeutic agents during balloon angioplasty.

Cell-free arterial grafts: morphologic characteristics of aortic isografts, allografts, and xenografts in rats

PURPOSE

Chronic rejection of arterial allografts and xenografts results in arterial wall dilation and rupture, making them unsuitable for long-term arterial replacement in vascular surgery. In the arterial wall, as in other organs, the cells probably carry major antigenic determinants. Arterial wall cellular components can be removed by detergent treatment to produce a graftable matrix tube.

METHODS

We compared the patency and macroscopic and microscopic morphologic changes that occurred in sodium dodecyl sulfate (SDS)-treated and untreated arterial isografts, allografts, and xenografts 2 months after implantation in rats. We quantified elastin, collagen, and nuclear density in the three layers of the graft wall (intima, media, and adventitia) by morphometric methods. The SDS treatment removed endothelial and smooth muscle cells and cells in the adventitia but preserved elastin and collagen extracellular matrix.

RESULTS

All arterial xenografts, whether SDS treated or untreated, were aneurysmal 2 months after grafting, with loss of the medial cellular and extracellular components. In allografts, SDS treatment prevented dilation, reduced adventitial inflammatory infiltration, and preserved medial elastin. The SDS-treated allografts had an evenly distributed, noninflammatory intimal thickening that was richer in elastin fibers than that in untreated allografts.

CONCLUSIONS

These results suggest an interspecies, but not an intraspecies, graft antigenicity of arterial extracellular matrix. The SDS treatment prevented chronic rejection of the arterial allograft and led to the proliferation of an elastin-rich and adapted intima.

Effects of thermal exposure on binding of heparin in vitro to the arterial wall and to clot and on the chronic angiographic luminal response to local application of a heparin film during angioplasty in an in vivo rabbit model

Experimentally, heparin inhibits mechanisms that promote fibrosis, neointimal cellular proliferation, and thrombin bound to fibrin at the surface of intraluminal thrombus, but only in relatively high concentrations. A preliminary hypothesis was tested and confirmed in vitro that initial binding of 3H-heparin to mechanically injured porcine aorta is concentration-dependent over a 1,000-50,000 units/ml range (r = 0.9). The hypothesis was then tested in vitro that thermal exposure during contact of heparin to arterial tissue and to clot would enhance binding of the drug. 3H-heparin binding to clot, whole blood particulates, and washed erythrocytes was markedly enhanced by exposure to temperatures > 70 degrees C. Thermal exposure (80 degrees C x 40 s) also enhanced tissue persistence of the drug within porcine aorta subjected to a shear rate of 1,100(-1) in an annular Baumgartner chamber perfused with normal saline at 37 degrees C for 48 h. Heparin in vitro anticoagulant activity persisted after thermal exposure and binding to tissues. A new method was developed for local application of a heparin film that provides a maximum concentration with a tolerable systemic dose during an angioplasty procedure. In an in vivo rabbit model of mural fibrosis after iliac artery angioplasty, the 1-month mean angiographic luminal diameter loss (23% compared to the acute postangioplasty result by computer image analysis) in response to conventional balloon angioplasty (BA) and laser balloon angioplasty (LBA) was the same (P > 0.05). Local application of a heparin film (3,000 units at a concentration > 100,000 units/g), however, reduced the mean % loss in diameter 1 month after LBA (12%), but not after BA (29%), compared to arteries subjected to angioplasty without local heparin (P < .05). The results are consistent with the hypothesis that thermal energy enhances heparin binding to tissues and that local application of a heparin film favorably modulates arterial luminal responses to LBA, but not to BA, in this animal model.