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S R Hanson

Publications and source records attributed to S R Hanson.

At least 73 records · Page 4Linked to original sources
PubMed1995

Thrombin hypothesis of thrombus generation and vascular lesion formation.

Thrombin plays a central role in vascular lesion formation. It is the principal mediator of thrombogenesis, which is interrupted when direct antithrombins (including hirudin and its synthetic peptide analogs), thrombin receptor antagonist peptides, or thrombin generation inhibitors (including active-site inhibited factor VIIa, recombinant tick anticoagulant peptide, and omega-3 fatty acids) are used to block thrombin. Thrombin is also a potent growth factor, initiating smooth muscle cell proliferation at injury sites. In baboons, this reaction is 80% reduced by hirudin (p < 0.01). Thrombin also plays a role in modulating the effects of other growth factors such as platelet-derived growth factor (PDGF). Thus, Phe-Pro-Arg-CH2Cl prevents expression in baboons of PDGF-A mRNA induced by vascular injury due to balloon angioplasty; untreated mechanical injury results in a 3-fold increase in PDGF-A mRNA expression. Thrombin also regulates inflammatory processes, inducing expression both of leukocyte adhesion molecules and of their counterreceptors by endothelium.

Animals↗
PubMed1995

Boundary layer infusion of heparin prevents thrombosis and reduces neointimal hyperplasia in venous polytetrafluoroethylene grafts without systemic anticoagulation.

PURPOSE: Recently, we designed and characterized a novel polytetrafluoroethylene-based local drug delivery device that selectively concentrates infused pharmacologic agents specifically within those blood layers adjacent to the graft wall and at downstream anastomotic sites. In this study we locally administered heparin with this approach and evaluated its effect on graft patency and neointimal hyperplasia formation in a rabbit model of inferior vena cava replacement. METHODS: Twelve animals were evenly assigned either to a control group infused with saline solution or to a treatment group infused with heparin for 14 days. Bromodeoxyuridine labeling was used to assess vascular cell proliferation. RESULTS: All grafts in the control group were occluded at 14 days. All grafts in the heparin-treated group remained patent, although there was no significant difference in systemic activated partial thromboplastin time measurements taken before and during the infusion of heparin (p > 0.5). In the treatment group, heparin reduced neointimal thickness, neointimal area, and the bromodeoxyuridine labeling index by 88%, 95%, and 72%, respectively (p < 0.01), at the locally treated downstream anastomosis as compared with the untreated upstream anastomosis. CONCLUSION: These data demonstrate that the local boundary layer infusion of heparin significantly increases overall inferior vena cava graft patency (p = 0.014) and markedly reduces downstream anastomotic neointimal hyperplasia and cell proliferation. This approach may represent an attractive strategy for antithrombotic therapy in venous replacement with synthetic graft materials.

Animals↗
PubMed1994

Alternative splicing of the mRNA encoding baboon glycoprotein receptor GPIIb.

The cloning and characterization of cDNAs encoding the cell-surface-specific integrin receptors of baboon platelets has been undertaken to provide species-specific probes. These will be used to investigate the expression and distribution of these receptors among primate species. Clones GPIIb-16 and GPIIb-3, encoding portions of the baboon glycoprotein GPIIb, were isolated from a cDNA library derived from baboon platelet mRNA. GPIIb-3 includes an insert of 43 bp, when compared to GPIIb-16 or human GPIIb. This insert is the result of alternative processing of mRNA. The probable origin of the inserted bases is the 3' end of the intron preceeding exon 28 of the gene. A different product of alternative splicing has been reported in this same region of the human GPIIb sequence, suggesting that this location is susceptible to wobble in the intron-exon junctions. The projected shift in the reading frame of the baboon GPIIb-3 cDNA would give a radically altered C terminus of the deduced amino-acid sequence, and the possibility of a novel functional peptide on the platelet surface.

Alternative Splicing↗
PubMed1994

Relative antithrombotic effects of monoclonal antibodies targeting different platelet glycoprotein-adhesive molecule interactions in nonhuman primates.

The relative antithrombotic effectiveness of targeting glycoprotein (GP) Ib-dependent versus GPIIb-IIIa-dependent platelet interactions has been determined in baboons by measuring thrombus formation after infusing comparable antihemostatic doses of anti-von Willebrand factor (vWF) monoclonal antibody (MoAb) BB3-BD5, anti-GPIb MoAb AP1, and anti-GPIIb-IIIa MoAb LJ-CP8 under conditions of arterial and venous flow (shear rates of 750 to 1,000 seconds-1 and 100 seconds-1, respectively). Thrombus formation was quantified as 111In-platelet deposition and 125I-fibrin accumulation on segments of collagen-coated tubing interposed in chronic exteriorized arteriovenous (AV) shunts for 40 minutes. In vitro, anti-vWF MoAb BB3 BD5 (IgG) and anti-GPIb MoAb AP1 [IgG or F(ab)2 fragments] inhibited ristocetin-induced platelet aggregation (IC50 50 nmol/L and 1 mumol/L, respectively), but neither of these MoAbs blocked platelet aggregation induced by adenosine diphosphate (ADP) (P > .5). Conversely, anti-GPIIb-IIIa MoAb LJ-CP8 inhibited platelet aggregation induced by ADP (IC50 1 mumol/L, but failed to block ristocetin-induced platelet aggregation (P > .5). In vivo, the intravenous infusion of anti-vWF MoAb BB3 BD5 or anti-GPIIb-IIIa MoAb LJ-CP8 into baboons at doses that abolished corresponding agonist-induced aggregation ex vivo (bolus injections of 0.5 mg/kg and 10 mg/kg, respectively) prolonged template bleeding times from baseline values of 4.0 +/- 0.3 minutes to > 27 +/- 4 minutes, and to > 26 +/- 4 minutes, respectively (P < .001 in both cases), without affecting the peripheral platelet count (P > .5). However, injection of anti-GPIb MoAb AP1 [10 mg/kg as IgG or 1 mg/kg as F(ab)2 fragments] produced immediate irreversible thrombocytopenia (< 40,000 platelets/microL). Anti-GPIIb-IIIa MoAb LJ-CP8 abolished platelet deposition and fibrin accumulation on collagen segments under both arterial and venous flow conditions (P < .01 in all cases), whereas MoAb BB3 BD5 produced minimal inhibition of platelet deposition and no decrease in fibrin accumulation at arterial shear rates and undetectable antithrombotic outcomes at low shear. Thus, inhibiting GPIIb-IIIa-dependent platelet recruitment abrogates both thrombus formation and platelet hemostatic function at both venous and arterial shear rates. By contrast, interfering with GPIb-vWF-dependent platelet interactions abolishes platelet hemostatic function without producing corresponding antithrombotic effects.

Animals↗
PubMed1994

Local delivery of a synthetic antithrombin with a hydrogel-coated angioplasty balloon catheter inhibits platelet-dependent thrombosis.

OBJECTIVES: This study evaluated the efficacy of local administration of an antithrombin agent with a hydrogel-coated percutaneous transluminal coronary angioplasty balloon catheter. BACKGROUND: Intravenous infusion of antithrombin compounds has been shown to inhibit platelet-dependent thrombosis. However, hemorrhage is a common side effect associated with the systemic administration of antithrombin compounds. METHODS: The potent, irreversible thrombin inhibitor D-Phe-L-Pro-L-Arginyl chloromethyl ketone (PPACK) was used to inhibit thrombus formation in chronic porcine arteriovenous shunts. Platelet deposition was quantitated with gamma camera imaging of 111In-labeled platelets. RESULTS: Intravenous administration of PPACK in swine, in doses sufficient to maximally inhibit thrombus formation, was associated with prolongation of bleeding parameters. The inhibition of thrombosis associated with intravenous PPACK was dose related. The amount of intravenous PPACK necessary for maximal inhibition of thrombus formation for a period of 45 min was 16.9 mg. In contrast, local delivery of PPACK with a hydrogel-coated angioplasty balloon deployed at the site of the thrombus inhibited platelet deposition for at least 45 min after the balloon was removed. Using 3H-labeled PPACK, the calculated amount of PPACK delivered was 33.5 micrograms. There was no change in bleeding time or activated partial thromboplastin time when swine received an intravenous bolus greater than the total amount of PPACK adsorbed onto the balloon (70 micrograms). CONCLUSIONS: These results suggest that in this model, a hydrogel-coated coronary angioplasty balloon catheter can be used to deliver enough antithrombin agent to inhibit platelet-dependent thrombosis for at least 45 min at doses that are several orders of magnitude less than those required for systemic administration. In addition, local delivery can provide effective inhibition of thrombus formation without alteration of bleeding parameters.

Amino Acid Chloromethyl Ketones↗
PubMed1994

Platelet thromboembolism.

Platelet-dependent thrombosis and subsequent embolization are major causes of cerebral ischaemia. Beside aspirin which irreversibly blocks platelet cyclo-oxygenase, several other substances interfere in different platelet metabolic pathways and block platelet adhesion and aggregation. We found in an experimental model using non-human primates that a specific peptide inhibitor blocking GP IIb/IIIa platelet receptor which binds fibrinogen completely, prevents the retention of embolized platelet aggregates in the cerebral circulation. As thrombin may play a key role for platelet activation in vivo leech-derived hirudin, a direct thrombin inhibitor as well as activated protein C which limits thrombin production and also prevents platelet dependent thrombus formation very effective. We demonstrated in the same non-human primate model of platelet embolization that the amount of retention of platelet emboli in the vascular bed depends on the nature of the vasculature. For example, platelet emboli were cleared very quickly from brain microcirculation, whereas platelet embolization into the lower limb via the femoral artery caused a significantly longer retention of the embolized material. Such specific mechanisms may be caused by different levels of local vasodilators as PGI2 or EDRF.

Animals↗
PubMed1994

A scaling law for wall shear rate through an arterial stenosis.

Atherosclerosis of the human arterial system produces major clinical symptoms when the plaque advances to create a high-grade stenosis. The hemodynamic shear rates produced in high-grade stenoses are important in the understanding of atheromatous plaque rupture and thrombosis. This study was designed to quantify the physiologic stress levels experienced by endothelial cells and platelets in the region of vascular stenoses. The steady hemodynamic flow field was solved for stenoses with percent area reductions of 50, 75, and 90 percent over a range of physiologic Reynolds numbers (100-400). The maximum wall shear rate in the throat region can be shown to vary by the square root of the Reynolds number. The shear rate results can be generalized to apply to a range of stenosis lengths and flow rates. Using dimensions typical for a human carotid or coronary artery, wall shear rates were found to vary from a maximum of 20,000 s-1 upstream of the throat to a minimum of -630 s-1 in the recirculation zone for a 90 percent stenosis. An example is given which illustrates how these values can be used to understand the relationship between hemodynamic shear and platelet deposition.

Arteriosclerosis↗
PubMed1994

Local delivery of an antithrombin inhibits platelet-dependent thrombosis.

BACKGROUND: Platelet-dependent thrombosis can be effectively inhibited by intravenous administration of direct thrombin antagonists. However, an increased propensity for abnormal bleeding has been associated with systemic administration of these agents. The goal of this study was to determine whether local delivery of a potent thrombin inhibitor, D-Phe-L-Pro-L-Arg chloromethyl ketone (PPACK), could inhibit platelet-dependent thrombosis without altering systemic hemostatic function. METHODS AND RESULTS: Thrombus formation was measured by quantitative imaging of 111In-labeled platelet deposition on segments of thrombogenic vascular graft interposed in arteriovenous shunts in a porcine model. Intravenous administration of PPACK inhibited platelet deposition at a dose of 12.5 micrograms/kg per minute, which was associated with significant prolongations of both template bleeding times and activated partial thromboplastin times. By contrast, local infusion of PPACK at a dose of 0.02 micrograms/kg per minute (ie, a 600-fold smaller dose) into the fluid boundary layer at the interface between flowing blood and the thrombogenic segment produced equivalent inhibition of platelet deposition without prolonging either the bleeding time or the activated partial thromboplastin time. In addition, static exposure of a mural thrombus to solutions of PPACK at concentrations > or = 2.5 mg/mL for 15 minutes produced sustained inhibition of platelet-dependent thrombosis with no change in hemostatic measurements. CONCLUSIONS: These results indicate that local delivery of the direct antithrombin PPACK, by either boundary layer infusion or static application techniques, effectively inhibits platelet-dependent thrombosis at doses that are several orders of magnitude less than the systemic dose required for an equivalent antithrombotic effect. In contrast to the systemic administration of PPACK, local delivery produced maximal inhibition of thrombosis without alterations in hemostasis.

Amino Acid Chloromethyl Ketones↗
PubMed1994

Characterization of thrombin receptor expression during vascular lesion formation.

Blood vessels respond to injury by initiating cell proliferation and migration that result in vascular lesion formation. To determine the roles of thrombin and the thrombin receptor in this process, we characterized thrombin receptor expression in normal and injured arteries, thrombin receptor-mediated smooth muscle cell mitogenesis, and the regulation of thrombin receptor mRNA expression in vitro. Thrombin receptor mRNA was not detected in normal rat or baboon arteries by in situ hybridization. Immunohistochemistry using an antithrombin receptor antibody (TR-R9), directed against the thrombin cleavage site of the rat aortic smooth muscle cell thrombin receptor, revealed low-level staining for thrombin receptor protein in endothelial cells and smooth muscle cells of normal arteries. In contrast, balloon catheter injury increased thrombin mRNA expression in medial smooth muscle cells within 6 hours. This increased thrombin receptor expression continued within the media and in neointimal cells throughout vascular lesion formation, predominantly in areas of active cell proliferation. In vitro, alpha-thrombin stimulates rat aortic smooth muscle cell proliferation in a concentration-dependent manner. That thrombin receptor activation is required for the mitogenic response was confirmed by demonstrating that the polyclonal antibody TR-R9 inhibits thrombin-induced cell proliferation. Thrombin receptor mRNA synthesis was induced by both basic fibroblast growth factor (maximal stimulation of 1.8-fold at 1 hour) and platelet-derived growth factor (maximal stimulation of 2.4-fold at 8 and 24 hours) in quiesced cultured rat aortic smooth muscle cells. In summary, upregulation of smooth muscle cell thrombin receptor expression occurs very early after vascular injury and continues throughout neointimal development.(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty↗
PubMed1994

Reaction to injury following balloon angioplasty and intravascular stent placement in the canine femoral artery.

Intravascular stents are used clinically as an adjunct to coronary and iliac angioplasty. This study was performed to evaluate the thrombogenicity and intimal hyperplasia incited by stents deployed in non-injured and in balloon-injured femoral arteries in the canine model. Medinvent stents (4 mm) were placed in the femoral arteries bilaterally in five mongrel dogs via cut down. This was preceded by balloon catheter angioplasty of the stent site on one side. Platelet deposition was measured at 30, 60, and 90 minutes and at 24 and 48 hours after stent placement, using gamma camera imaging of Indium111 platelets. The animals were killed after 2 months using a pressure perfusion technique, and the stents harvested. All vessels were patent at the time of harvest. Neointimal thickness was measured by computer image analysis. Platelet deposition was significantly increased on the angioplastied side compared to the non-angioplastied side at 60 minutes (5.67 x 10(9) +/- 1.4 versus 2.17 x 10(9) +/- 0.5 platelets/cm; P < 0.05), at 90 minutes (8.13 x 10(9) +/- 1.8 versus 2.33 x 10(9) +/- 0.6 platelets/cm; P < 0.05), and at 24 hours (stent-to-blood ratio = 15.86 +/- 6.3 versus 3.75 +/- 1.5; P < 0.05). Neointimal thickness was also significantly greater on the side of combined angioplasty and stent placement (0.45 +/- 0.21 mm versus 0.33 +/- 0.09 mm; P < 0.05). These results demonstrate that placement of intravascular stents in normal arteries is associated with a certain degree of thrombogenicity and formation of neointimal hyperplasia. Combining balloon angioplasty with stent placement significantly augments both thrombogenicity and production of intimal hyperplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Balloon↗
PubMed1993

Human and baboon integrin beta 5 subunit-encoding mRNAs have alternative polyadenylation sites.

A cDNA probe, encoding part of the human integrin polypeptide, GPIIIa (beta 3), was used to screen a cDNA library derived from baboon smooth muscle polyadenylated mRNA. One cross-hybridizing clone, lacking the baboon equivalent of 478 bp of the human sequence, was found to be 98% similar to a human cDNA encoding the beta 5-chain of the receptor for vitronectin, a cell adhesion molecule. The baboon mRNA terminates at 3' position 212 nucleotides upstream from the polyadenylation site of the aligned human mRNA.

Amino Acid Sequence↗
PubMed1993

Antithrombotic effects of synthetic pentasaccharide with high affinity for plasma antithrombin III in non-human primates.

The pentasaccharide (PS) comprising the minimal heparin structure capable of binding with antithrombin III (ATIII) and exhibiting anti-factor Xa (anti-fXa) activity in plasma without producing detectable antithrombin activity, has been evaluated for its relative antithrombotic and antihemostatic effects in a baboon model combining both platelet-rich and fibrin-rich thrombosis. Thrombosis was produced in a two-component thrombogenic device incorporated into an exteriorized femoral arteriovenous (AV) shunt in baboons; the proximal component constituted a segment of collagen-coated tubing and induced platelet-rich arterial-type thrombus, while the distal component consisted of an expanded chamber producing static and disturbed flow and initiated fibrin-rich venous-type thrombosis. Thrombus formation was measured as the deposition of 111In-platelets and the accumulation of 125I-fibrin. PS was administered intravenously to maintain plasma anti-fXa activity at three different levels: a) low dose (LD) 0.3 +/- 0.1 U/ml; b) intermediate dose (ID) 0.6 +/- 0.1 U/ml; and c) high dose (HD) 5.6 +/- 0.4 U/ml. In untreated controls, thrombus formed rapidly, reaching a plateau by 40 min of 2.3 +/- 0.2 x 10(9) platelets and 0.62 +/- 0.04 mg fibrin deposited on the collagen segments, and 1.9 +/- 0.4 x 10(9) platelets and 3.3 +/- 0.4 mg fibrin accumulated in the chambers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Characterization of a cDNA encoding the beta-chain of baboon receptor glycoprotein GPIb.

A cDNA probe, encoding part of the baboon integrin polypeptide, GPIIb, was used to screen a cDNA library derived from baboon platelet polyadenylated mRNA. One cross-hybridizing clone was found to be 94% similar to a human cDNA encoding the beta-chain of the receptor for von Willebrand factor, a major component of the platelet-subendothelium attachment mechanism.

Amino Acid Sequence↗
PubMed1993

Lasting safe interruption of endarterectomy thrombosis by transiently infused antithrombin peptide D-Phe-Pro-ArgCH2Cl in baboons.

To evaluate the relative antithrombotic efficacy and hemostatic safety of antithrombin therapy for vascular thrombus formation at sites of mechanical vascular injury, we administered the potent and specific irreversible synthetic antithrombin D-PHE-PRO-ARG chloromethyl ketone (D-FPRCH2Cl) after performing carotid endarterectomies in baboons. The continuous intravenous infusion of D-FPRCH2Cl, 100 nmol/kg per minute for 1 hour, abolished acute carotid endarterectomy thrombosis for at least 48 hours. The plasma level of D-FPRCH2Cl during the infusion was maintained steady at 7.2 +/- 0.9 mumol/L, but decreased rapidly after discontinuing its infusion (T50 17 minutes). Platelet deposition, measured in real time using autologous 111In-platelet scintillation camera imaging, was 1.51 +/- 0.40 x 10(8) platelet/cm in the 14 treated animals 90 minutes postoperatively, compared with 11.7 +/- 1.16 x 10(8) platelet/cm in 14 heparin-treated controls (P < .002). The antithrombotic benefit was equivalent for treatment begun either 5 minutes before (nine animals) or 15 minutes after (five animals) reestablishing flow in the operated vessel, ie, 1.59 +/- 0.36 x 10(8) platelet/cm versus 1.35 +/- 0.51 x 10(8) platelet/min, respectively; P > .5. Endarterectomy thrombosis remained decreased for at least 48 hours postoperatively, as determined by the ratio between net 111In-platelet radioactivity at the endarterectomized site versus whole blood (ratio 0.82 +/- 0.25 in the treatment group v 3.03 +/- 0.51 in heparin controls at 90 minutes, P < .005; and 0.85 +/- 0.23 v 3.25 +/- 0.48 at 48 hours, P < .002). The marked reduction in endarterectomy thrombosis in treated animals at 48 hours was confirmed by scanning electron microscopy. Thrombin activity formed rapidly and became immediately bound to thrombus on thrombogenic segments in untreated control studies; treatment with D-FPRCH2Cl irreversibly inactivated the thrombus-bound thrombin. Hemostatic function, as measured by bleeding time (BT), activated partial thromboplastin time (APTT), and prothrombin time (PT) was impaired throughout the intravenous administration of D-FPRCH2Cl (BT > 30 minutes, APTT > 150 seconds, PT > 50 seconds); BT, APTT, and PT values were normal 30 minutes after discontinuing the infusions. As expected, blood loss into the surgical wound was substantial in nine animals receiving therapy initiated before restoring flow in the operated vessel (mean 95 mL, range 45 to 130 mL). By contrast, beginning D-FPRCH2Cl therapy in five animals 15 minutes after restoring arterial flow, a time when surgical hemostasis had been achieved, prevented excessive blood loss (mean 15 mL, range 10 to 35 mL; P < .01 compared with earlier treatment) without compromising the antithrombotic effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Chloromethyl Ketones↗
PubMed1993

Interruption of vascular thrombosis by bolus anti-platelet glycoprotein IIb/IIIa monoclonal antibodies in baboons.

PURPOSE: Because the platelet membrane receptor glycoprotein IIb/IIIa plays a central role in the recruitment of platelets into forming thrombus, therapeutic inhibition of this receptor complex may be particularly useful to prevent thrombosis after small vessel arterial manipulation. METHODS: The relative hemostatic safety and antithrombotic efficacy for thrombus formation at sites of endarterectomy and implanted prosthetic vascular graft of a murine monoclonal antibody (LJ-CP8) against platelet glycoprotein IIb/IIIa have been determined in baboons after bolus injections in doses (10 mg/kg) that block platelet receptor function for fibrinogen and other adhesive glycoproteins (absent platelet aggregation and bleeding times > 30 minutes without affecting circulating platelet counts). RESULTS: Thrombus formation was eliminated by LJ-CP8 at sites of surgical endarterectomy in fresh segments of homologous aorta incorporated into chronic exteriorized arteriovenous femoral shunts (accumulation of indium 111-labeled platelets fell from 4.40 +/- 0.89 x 10(9) platelets/cm in control animals [n = 6] to 0.23 +/- 0.01 x 10(9) platelets/cm in treated animals [n = 4]; p < 0.005). The formation of thrombus was also abolished by LJ-CP8 at sites of 1 cm prosthetic vascular grafts (4 mm inner diameter polytetrafluoroethylene grafts) interposed into common carotid arteries (deposition of indium 111-labeled platelets decreased from 2.57 +/- 0.43 x 10(9) platelets/cm [n = 5] to 0.16 +/- 0.06 x 10(9) platelets/cm, [n = 4]; p = 0.004). However, LJ-CP8 injections produced substantial bleeding in the surgical wound during the first few hours after operation. Thirty days after operation all four graft implants were patent in JJ-CP8-treated animals compared with two of five in control animals (p = 0.06). CONCLUSIONS: We conclude that profound inhibition of platelet glycoprotein IIb/IIIa receptor function by single bolus injection of LJ-CP8 monoclonal antibody transiently abolishes platelet hemostatic function, eliminates acute thrombus formation at sites of endarterectomy and prosthetic vascular graft implants, and may improve vascular patency.

Animals↗