Current perspectives on venous disease

24th Annual Meeting of the American Venous Forum Orlando, FL, USA, 8-11 February 2012: The American Venous Forum unites authorities on all facets of venous disease, the pathophysiology of venous disease and its treatment. The goal of this meeting was to educate attendees about current and novel clinical strategies to effectively manage venous disease.

Abstract 196: Matrix Metalloproteinases Regulation in Thrombus Resolution Is Independent of TGF-β in a PAI-1 Ko Mouse Model of Venous Thrombosis

Introduction: Plasminogen activator inhibitor (PAI-1) is the primary regulator of urokinase (u-PA) and tissue (t-PA) plasminogen activators. Observations in mice with impaired fibrinolysis have demonstrated an alternate pathway of thrombus resolution by matrix metalloproteinase (MMP)- 9 and 2. TGF-β is a potent inducer of TIMP-1 expression and is found in both thrombus and vein wall post-thrombosis.

Hypothesis: PAI-1 deficiency and resulting hyperfibrinolytic state will improve thrombus resolution and result in reciprocal downregulation of MMP-2 and MMP-9 via TGF-beta induction of TIMP-1, resulting in decreased vein wall fibrosis.

Methods: Inferior vena cava (IVC) ligation was performed in wild-type (WT) mice (N=194) and PAI-1 deficent mice (N=164). IVC, thrombus and blood samples were collect at 2, 6 and 14 days post procedure. The IVC and thrombus were assessed for thrombus weight and samples collected for zymography (MMP-2 and MMP-9), ELISA (TIMP-1, TGF-β) and histology.

Results: PAI-1 deficient mice had similar thrombus weight (TW) versus WT at 2 days, but smaller at days 6 (p<0.0001) and 14 (p=0.0085). In thrombus and vein wall (VW), active MMP-9 was decreased in acute thrombosis (p<0.0001), and MMP-2 was decreased during late thrombus resolution (p<0.05). TIMP-1 levels in VW were elevated across all time points (p<0.05), whereas VW TGF-beta was not different compared to WT. Neutrophils were decreased at day 2 (p = 0.0309) and monocytes decreased at day 14 (p = 0.0028).

Conclusions: (1) PAI-1 deficient mice exhibit a hyperfibrinolytic phenotype with normal thrombotic response to IVC ligation, but improved thrombus resolution when compared to WT mice. (2) MMP-9 and MMP-2 were suppressed, confirming a reciprocal relationship between plasmin and MMP activation as mediators of thrombus resolution. (3) TIMP-1 production was elevated in vein wall independent of TGF-beta. (4) Decreased neutrophils at day 2 correlated with decreased MMP-9 and decreased monocytes at day 14 correlated with decreased MMP-2, suggesting a plasmin-induced inhibition of leukocyte recruitment. (5) Final histology showed no difference in vein wall fibrosis or thickness at chronic time points, indicating that improved thrombus resolution does not lessen vein wall fibrosis.

Abstract 27: Galectin-3 Binding Protein: A New Factor Promoting Venous Thrombosis

Galectin-3 binding protein (Gal-3BP) was detected in procoagulant microparticles from mice and patients with venous thrombosis (VT), in prior studies from our laboratory. However, the mechanistic role of Gal-3BP and Galactin-3 (Gal-3) in the pathophysiology of thrombosis is unknown. Our hypothesis is that Gal-3BP and Gal-3 are critical to thrombus formation.

Methods: Mice : Using our inferior vena cava ligation mouse model of VT, microparticle samples from thrombosed and non-thrombosed wild type mice were analyzed for Gal-3BP. We then either neutralized Gal-3BP, using an antibody (Anti-M-Gal-3BP), or utilized Gal-3 knock-out (Gal-3 KO) mice, compared to mice given saline as controls (NaCl). We evaluated thrombus weight (TW), inflammatory cell counts, and the cell source of the molecules Gal-3BP and Gal-3 using western blot.

Patients: Microparticles and plasma samples from patients who were positive or negative for VT were tested for Gal-3BP using ELISA.

Results: Mice : Two days after thrombosis, blocking Gal-3BP significantly reduced both vein wall inflammatory cells ( p =0.0369) and TW ( p =0.0024), compared to NaCl. In Gal-3 KO mice, TW was significantly smaller versus controls ( p =0.0061). We found Gal-3BP on microparticles and platelets while Gal-3 was on monocytes. Patients : Gal-3BP was significantly elevated in microparticles ( p =0.0495) and in plasma ( p =0.0400), versus patients negative for VT. Conclusions: We demonstrated a clear link between Gal-3BP and VT, in both mice and patients. This is the first time that Gal-3BP has been shown to be involved with thrombus formation, making it a promising biomarker and potential target for therapeutic interventions of VT.

Critical review of mouse models of venous thrombosis

Deep vein thrombosis and pulmonary embolism are a significant health care concern, representing a major source of mortality and morbidity. In order to understand the pathophysiology of thrombogenesis and thrombus resolution, animal models are necessary. Mouse models of venous thrombosis contribute to our understanding of the initiation, propagation, and resolution of venous thrombus, as well as allow for the evaluation of new pharmaceutical approaches to prophylaxis and treatment of deep vein thrombosis. In this work we review the ferric chloride model, the inferior vena cava ligation model, the inferior vena cava stenosis models, and the electrolytic inferior vena cava model and compare their advantages and disadvantages.

Inflammation and thrombosis: new insights

Vessel wall endothelial damage initiates a local inflammatory response, which promotes a prothrombotic state driven by tissue factor, adhesion molecules, and pro-inflammatory cytokines. Understanding how natural inflammatory mechanisms promote a procoagulant state, may lead to the development of new pharmacological interventions targeted at thrombosis.

Myeloid cell tissue factor does not contribute to venous thrombogenesis in an electrolytic injury model

INTRODUCTION

Tissue factor (TF) is a potent initiator of the extrinsic coagulation cascade. The role and source of TF in venous thrombotic disease is not clearly defined. Our study objective was to identify the contribution of myeloid cell TF to venous thrombogenesis in mice.

MATERIALS AND METHODS

The mouse electrolytic inferior vena cava model was used to induce thrombosis. The following groups of mice were used (1) TF(flox/flox)LysMCre(+) mice that have reduced TF expression in myeloid cells, (2) TF(flox/flox)LysMCre(-) littermate controls, (3) Wild type mice given a monoclonal anti-mouse TF antibody (1H1) to inhibit TF activity, and (4) Wild type mice given rat IgG. Evaluations at baseline, day 2, and day 6 post thrombosis included thrombus weight, vein wall inflammatory cell migration, vein wall TF mRNA, and plasma D-dimer levels.

RESULTS

Inhibition of TF significantly decreased thrombus weight 2days post venous thrombosis. In contrast, TF(flox/flox)LysMCre(+) had no change in thrombus weight when compared to littermate controls. The absence of myeloid cell TF did not affect infiltration of neutrophils or monocytes into the vein wall. TF mRNA expression in the vein wall decreased at 2days but then returned to baseline levels by 6days post thrombosis. D-dimer levels peaked at 2days post thrombosis in mice with or without myeloid cell TF.

CONCLUSIONS

TF is important in the formation of venous thrombi in the macrovasculature. However, TF expression by myeloid cells does not significantly contribute to venous thrombogenesis in this model.

Impaired fibrinolytic system in ApoE gene-deleted mice with hyperlipidemia augments deep vein thrombosis

BACKGROUND

Hyperlipidemia increases the level of blood plasminogen activator inhibitor-1 (PAI-1) that is responsible for regulating fibrinolysis by inhibiting both urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA). While this fibrinolytic pathway is well known, the role of PAI-1 in venous thrombosis (VT) under hyperlipidemic conditions has not been fully established. We sought to determine the effects of PAI-1 in an in vivo hyperlipidemic model of VT.

METHODS

C57BL/6 wild-type (WT) mice, apolipoprotein E gene-deleted mice (ApoE-/-) having hyperlipidemia, and PAI-1 gene-deleted (PAI-1-/-) mice were used in this study. Inferior vena cava (IVC) ligation below the level of the renal veins was performed to create a stasis VT. Endpoints included measuring acute thrombosis (day 2) and chronic thrombosis (days 6 and 14). At euthanasia, blood samples were collected for plasmin and PAI-1 activity. In addition, the IVC and its thrombus were evaluated for thrombus weight (TW), u-PA activity, and differential leukocyte count while the vein wall only was analyzed for monocyte chemoattractant protein-1 (MCP-1), matrix metalloproteinase (MMP) 2, and MMP-9.

RESULTS

Compared to WT at day 2, ApoE-/-mice demonstrated a statistically significant 14% increase in TW (P < .05) and a significant 41% increase in circulating PAI-1 activity (P < .05), while showing a trend of decreased plasmin activity. In addition, TW in ApoE-/-mice was 45% higher than PAI-1-/-mice at day 2 (P < .05), 33% at day 6 (P < .01), and 41% at day 14 (P < .01). ApoE-/-mice exhibited undetectable levels of u-PA in both vein wall and thrombus, compared to WT, at all time points. Also, vein wall MMP-2 was significantly decreased by 64% at day 6 (P < .01) and 58% at day 14 (P < .05). MMP-9 was significantly decreased by 71% at day 2 (P < .01) and 48% at day 6 (P < .01), in ApoE-/-mice compared to WT mice. In addition, in ApoE-/-mice, MCP-1 was significantly decreased by 38% at day 2 (P < .01) and 67% at day 6 (P < .01) vs WT mice. As expected in ApoE mice, following a decrease in MCP-1, monocyte recruitment was significantly decreased at days 6 (P < .01) and 14 (P < .05).

CONCLUSIONS

A significant increase of circulating PAI-1 levels in hyperlipidemic mice correlated with an early increase in TW due to impaired fibrinolysis. The undetectable levels of u-PA in ApoE-/-mice correlated to a decrease in vein wall MMP-2, MMP-9, MCP-1, and a decrease in monocyte recruitment diminishing thrombus resolution.

Electrolytic inferior vena cava model (EIM) of venous thrombosis

Animal models serve a vital role in deep venous thrombosis (DVT) research in order to study thrombus formation, thrombus resolution and to test potential therapeutic compounds (1). New compounds to be utilized in the treatment and prevention of DVT are currently being developed. The delivery of potential therapeutic antagonist compounds to an affected thrombosed vein has been problematic. In the context of therapeutic applications, a model that uses partial stasis and consistently generates thrombi within a major vein has been recently established. The Electrolytic Inferior vena cava Model (EIM) is mouse model of DVT that permits thrombus formation in the presence of continuous blood flow. This model allows therapeutic agents to be in contact with the thrombus in a dynamic fashion, and is more sensitive than other models of DVT (1). In addition, this thrombosis model closely simulates clinical situations of thrombus formation and is ideal to study venous endothelial cell activation, leukocyte migration, venous thrombogenesis, and to test therapeutic applications (1). The EIM model is technically simple, easily reproducible, creates consistent thrombi sizes and allows for a large sample (i.e. thrombus and vein wall) which is required for analytical purposes.

Mouse complete stasis model of inferior vena cava thrombosis

Venous thromboembolism (VTE) includes both deep vein thrombosis (DVT) and pulmonary embolism (PE). In the United States (U.S.), the high morbidity and mortality rates make VTE a serious health concern (1-2). After heart disease and stroke, VTE is the third most common vascular disease (3). In the U.S. alone, there is an estimated 900,000 people affected each year, with 300,000 deaths occurring annually (3). A reliable in vivo animal model to study the mechanisms of this disease is necessary. The advantages of using the mouse complete stasis model of inferior vena cava thrombosis are several. The mouse model allows for the administration of very small volumes of limited availability test agents, reducing costs dramatically. Most promising is the potential for mice with gene knockouts that allow specific inflammatory and coagulation factor functions to be delineated. Current molecular assays allow for the quantitation of vein wall, thrombus, whole blood, and plasma for assays. However, a major concern involving this model is the operative size constraints and the friability of the vessels. Also, due to the small IVC sample weight (mean 0.005 grams) it is necessary to increase animal numbers for accurate statistical analysis for tissue, thrombus, and blood assays such as real-time polymerase chain reaction (RT-PCR), western blot, enzyme-linked immunosorbent (ELISA), zymography, vein wall and thrombus cellular analysis, and whole blood and plasma assays (4-8). The major disadvantage with the stasis model is that the lack of blood flow inhibits the maximal effect of administered systemic therapeutic agents on the thrombus and vein wall.

Evaluation of soluble P-selectin as a marker for the diagnosis of deep venous thrombosis

OBJECTIVE

The combination of D-dimer and Wells score can exclude, but not confirm, the diagnosis of deep venous thrombosis (DVT). Since thrombosis and inflammation are interrelated, we evaluated the combination of soluble P-selectin (sPsel) with other inflammatory biomarkers for the diagnosis of DVT.

METHODS

Sixty-two positive and one hundred and sixteen patients with negative DVT, by duplex scan, were prospectively evaluated for sPsel, D-dimer, C-reactive protein (CRP), microparticles (MPs; total, leukocyte, and platelet-derived and tissue factor positive microparticles), and clinical Wells score.

RESULTS

Biomarkers and clinical scores that differentiated DVT positives from negatives were sPsel (87.3 vs 53.4 ng/mL, P < .0001), D-dimer (5.8 vs 2.1 mg/ L, P < .0001), CRP (2.1 vs 0.8 μg/mL, P < .0005), and Wells score (3.2 vs 2.0, P < .0001). For MP analysis, platelet-derived MPs were found to differentiate DVT from negatives. Using multivariable logistic regression, a combination of sPsel and Wells score could establish the diagnosis of DVT (cut point ≥ 90 ng/mL + Wells ≥ 2), with a specificity of 96% and positive predictive value (PPV) of 100%, and could exclude DVT diagnosis (cut point ≤ 60 ng/mL and Wells <2) with a sensitivity of 99%, a specificity of 33%, and a negative predictive value (NPV) of 96%.

CONCLUSION

This study establishes a biomarker and clinical profile combination that can both confirm and exclude the diagnosis of DVT.

Male mice have increased thrombotic potential: sex differences in a mouse model of venous thrombosis

INTRODUCTION

Our objectives were to characterize sex differences during venous thrombosis, using the electrolytic inferior vena cava model of the disease.

MATERIALS AND METHODS

Male and female C57BL/6 mice (6-8 weeks) underwent inferior vena cava thrombosis. Time points included 6 hours, day 2, day 6, and day 14 post surgery, along with surgically naïve true controls and surgical shams. Analyses included thrombus weight, vein wall morphometrics, vein wall protein and gene expression for P-selectin, interleukin-1β, and tumor necrosis factor-α; hematology, soluble P-selectin, and plasma microparticle tissue factor activity assays.

RESULTS

Male venous thrombi were significantly larger than females at days 2 (13.1 ± 1.0 vs. 6.8 ± 0.5 × 10(-3) grams, p < 0.01), 6 (10.4 ± 0.8 vs. 5.4 ± 0.5 × 10(-3) grams, p < 0.01) and 14 (6.3 ± 0.5 vs. 4.1 ± 0.3 × 10(-3) grams, p < 0.01). Both male and female mice exhibited significantly increased vein wall P-selectin at 6 hours, vs. true controls (p < 0.05). Males had increased vein wall interleukin-1β, versus females, at 6 hours (180.926 ± 24.596 vs. 60.417 ± 10.478 pg/mL, p < 0.05) and day 6 (76.966 ± 13.081 vs. 33.834 ± 4.198 pg/mL, p < 0.01). Males showed decreased tumor necrosis factor-α expression (-66 %) at 6 hours. Females had increased tumor necrosis factor-α expression at 6 hours (+541%) and day 6 (+539%). Both sexes demonstrated decreased peripheral platelets at 6 hours (p < 0.05), coinciding with thrombogenesis. Plasma P-selectin increased in both sexes, versus controls, through day 6 (p < 0.05).

CONCLUSIONS

Males had significantly larger venous thrombi than females. Sex differences in vascular anatomy and response to inflammation may influence thrombus formation in our mouse thrombosis model.

Noninvasive treatment of deep venous thrombosis using pulsed ultrasound cavitation therapy (histotripsy) in a porcine model

PURPOSE

This study evaluated histotripsy as a noninvasive, image-guided method of thrombolysis in a porcine model of deep vein thrombosis. Histotripsy therapy uses short, high-intensity, focused ultrasound pulses to cause mechanical breakdown of targeted soft tissue by acoustic cavitation, which is guided by real-time ultrasound imaging. This is an in vivo feasibility study of histotripsy thrombolysis.

METHODS AND MATERIALS

Acute thrombi were formed in the femoral vein of juvenile pigs weighing 30-40 kg by balloon occlusion with two catheters and thrombin infusion. A 10-cm-diameter 1-MHz focused transducer was used for therapy. An 8-MHz ultrasound imager was used to align the clot with the therapy focus. Therapy consisted of five cycle pulses delivered at a rate of 1 kHz and peak negative pressure between 14 and 19 MPa. The focus was scanned along the long axis of the vessel to treat the entire visible clot during ultrasound exposure. The targeted region identified by a hyperechoic cavitation bubble cloud was visualized via ultrasound during treatment.

RESULTS

Thrombus breakdown was apparent as a decrease in echogenicity within the vessel in 10 of 12 cases and in 7 cases improved flow through the vein as measured by color Doppler. Vessel histology found denudation of vascular endothelium and small pockets of hemorrhage in the vessel adventitia and underlying muscle and fatty tissue, but perforation of the vessel wall was never observed.

CONCLUSIONS

The results indicate histotripsy has potential for development as a noninvasive treatment for deep vein thrombosis.

Interleukin-6: a potential target for post-thrombotic syndrome

BACKGROUND

Deep vein thrombosis (DVT) and its associated sequelae, post-thrombotic syndrome (PTS), are significant health care problems in the United States. It is estimated that a maximum of 60% of patients diagnosed with DVT develop PTS, which is characterized by extensive perivenous and mural fibrosis. Interleukin-6 (IL-6) has been linked to fibrosis, and high circulating plasma levels have been found to increase the risk of developing DVT. The aim of this study was to elucidate the role of IL-6 in the progression of vein wall fibrosis by using a mouse model of DVT.

METHODS AND RESULTS

C57BL/6 mice (n = 136) were treated with either anti-IL-6 monoclonal antibody or control rat-immunoglobulin G. Thrombus was induced by using an inferior vena cava ligation model. The inferior vena cava and thrombus were harvested at days 2, 6, or 14 for thrombus weight, gene expression of IL-6 and/or C-C motif chemokine ligand 2 (CCL2), inflammatory cell recruitment, and morphometric analysis of vein wall fibrosis. Mice treated with anti-IL-6 had smaller thrombus weights at day 2, decreased vein wall gene expression and protein concentration of CCL2 at day 2, and impaired vein wall influx of monocytes from days 2 to 6, as compared with controls. Intimal thickness was reduced by 44% (p < 0.05) and vein wall collagen deposition was decreased by 30% at day 14 in the anti-IL-6 group (p < 0.05).

CONCLUSIONS

Neutralizing IL-6 throughout venous thrombogenesis decreased the production of CCL2, reduced monocyte recruitment, and decreased vein wall intimal thickness and fibrosis. These results suggest that IL-6 may serve as a therapeutic target to prevent the fibrotic complications seen in PTS.

Thrombogenesis with continuous blood flow in the inferior vena cava. A novel mouse model

Several rodent models have been used to study deep venous thrombosis (DVT). However, a model that generates consistent venous thrombi in the presence of continuous blood flow, to evaluate therapeutic agents for DVT, is not available. Mice used in the present study were wild-type C57BL/6 (WT), plasminogen activator inhibitor-1 (PAI-1) knock out (KO) and Delta Cytoplasmic Tail (DCT). An electrolytic inferior vena cava (IVC) model (EIM) was used. A 25G stainless-steel needle, attached to a silver coated copper wire electrode (anode), was inserted into the exposed caudal IVC. Another electrode (cathode) was placed subcutaneously. A current of 250 muAmps over 15 minutes was applied. Ultrasound imaging was used to demonstrate the presence of IVC blood flow. Analyses included measurement of plasma soluble P-selectin (sP-Sel), thrombus weight (TW), vein wall morphometrics, P-selectin and Von Willebrand factor (vWF) staining, transmission electron microscopy (TEM), scanning electron microscopy (SEM); and the effect of enoxaparin on TW was evaluated. A current of 250 muAmps over 15 minutes consistently promoted thrombus formation in the IVC. Plasma sP-Sel was decreased in PAI-1 KO and increased in DCT vs. WT (WT/PAI-1: p=0.003, WT/DCT: p=0.0002). Endothelial activation was demonstrated by SEM, TEM, P-selectin and vWF immunohistochemistry and confirmed by inflammatory cell counts. Ultrasound imaging demonstrated thrombus formation in the presence of blood flow. Enoxaparin significantly reduced the thrombus size by 61% in this model. This EIM closely mimics clinical venous disease and can be used to study endothelial cell activation, leukocyte migration, thrombogenesis and therapeutic applications in the presence of blood flow.

Proteomics of microparticles after deep venous thrombosis

BACKGROUND

Microparticles (MP) are submicron size membrane vesicles released from activated cells that are associated with thrombosis and inflammation. MP present diverse biological expressions that may be linked to a unique subset of proteins derived from their origin cells.

METHODS

To identify these proteins, plasma samples were taken from 9 patients with deep venous thrombosis (DVT) documented by duplex ultrasound, 9 with leg pain but negative for DVT by duplex, and 6 healthy controls without a history of thrombosis, for fold variation. MP were extracted from platelet-poor plasma, digested separately with trypsin and tagged using iTRAQ reagents. The digests were subjected to 2-D LC separation followed by MALDI tandem mass spectrometry. Peak lists were generated and searched against all human sequences. For protein identification, a minimum of two peptides at 95% confidence was required. Later, iTRAQ ratios were generated comparing relative protein levels of DVT patients to baseline. The proteomic analysis was performed twice for each blood sample. Proteins were considered elevated or depressed if the iTRAQ ratio (R) deviated by 20% change from normal and a p-value less than 0.05.

RESULTS

Two proteins (Galectin-3 Binding Protein, [Gal3BP], R=1.76 and Alpha-2 macroglobulin [A2M] R=1.57) were differentially expressed on DVT patients. Nine proteins were depleted including fibrinogen beta and gamma chain precursors (R=0.65).

CONCLUSIONS

These proteins influence thrombosis through inflammation, cell shedding, inhibition of fibrinolysis and hemostatic plug formation. Further studies are needed to confirm the mechanistic role of these proteins in the pathogenesis of venous thrombosis in humans.

Microparticle surface protein are associated with experimental venous thrombosis: a preliminary study

Microparticles are small membrane vesicles released from activated cells and are associated with thrombosis and inflammation. Microparticle contain a unique subset of surface protein derived form the parent cell and may be responsible for their diverse biological functions. To identify these proteins, juvenile baboons (Papio anubis, n = 4) underwent iliac vein thrombosis with 6-hour balloon occlusion. Plasma samples were taken at baselines and at 2 days postthrombosis for microparticle analysis. Microparticles were extracted from platelet-poor plasma, digest separately with trypsin and tagged using isobaric tagging for relative and absolute quantitation reagents. The digests were subjected to 2-dimensional liquid chromatographic separation followed by matrix-assisted laser desorption/ionization tandem mass spectrometry. Peak lists were generated and searched against all primate sequences. For protein identity, a minimum of 2 peptides at 95% confidence interval was required. Later, isobaric tagging for relative and absolute quantitation ratios were generated comparing relative protein level of day 2 to baseline. The proteomic analysis was performed twice for each blood sample, totaling 8 experiments. Proteins were considered elevated of depressed if the isobaris tagging for relative and absolute quantitation ratio deviated by 20% changes from normal and a P value less than .05. Significantly, 7 proteins were differentially expressed on day 2 compared to baseline, and appeared in at least 3 animals and regulated in at least 4 experiment. Among these 7 proteins, upregulated proteins include various forms of fibrinogen and alpha-1-antichymotrypsin and downregulated proteins include immunoglobulins. These proteins influence thrombosis and inflammation through hemostatic plug formation (fibrinogen), inhibiting neutrophil adhesion (alpha-1-antichymoptrypsin), and immunoregulation (immunoglobulins). Further studies are needed to confirm the mechanistic role of these proteins in the pathogenesis of venous thrombosis.

Enoxaparin treatment of spontaneous deep vein thrombosis in a chronically catheterized rhesus macaque (Macaca mulatta)

A chronically catheterized 14-y-old male rhesus macaque (Macaca mulatta) was reported for recurrent scrotal swelling. The scrotum was enlarged and warm to touch, and associated skin was noted to be lichenified on physical examination. The penis could not be extruded due to preputial swelling. Results from the following diagnostic tests were all unremarkable or within normal limits: scrotal aspirate, hematology, serum biochemistries, urinalysis, and radiography of the thorax, scrotum, and abdomen. Ultrasonography of lower extremities identified thrombi in bilateral iliac veins and left femoral vein. Collateral circulation surrounding the left femoral vein permitted some compensatory venous return. The left femoral vein of this animal had been catheterized approximately 2 mo before initial presentation. A coagulation panel revealed a positive D-dimer test, indicative of elevated levels of fibrin degradation products due to active thrombus breakdown. Enoxaparin sodium, a low-molecular-weight heparin for human use, was administered at 20 mg subcutaneously once daily for 10 d to treat occlusive venous thrombi. After enoxaparin treatment, the edema was greatly decreased. To achieve complete resolution, a second course of enoxaparin was administered 2 months after the first. Ultrasonography of the pelvic vasculature 6 mo after completion of therapy showed marked thrombus resolution, allowing for bilateral patency in the iliac and femoral veins. Follow-up evaluation revealed that D-dimer values were negative as well. This case demonstrates the novel application of the human medication enoxaparin to treat clinical signs of deep vein thrombosis in a chronically catheterized rhesus macaque.

Aging is associated with impaired thrombus resolution in a mouse model of stasis induced thrombosis

INTRODUCTION

To evaluate the effects of aging on venous thrombosis.

MATERIAL AND METHODS

Anesthetized male mice (C57BL/6, n=125) underwent complete inferior vena cava occlusion to produce venous thrombosis. Experimental groups included 11-month-old mice (OLD), 2-month-old mice (YOUNG), and age-matched non-thrombosed controls. Mice were euthanized and the following parameters were evaluated two days post-thrombosis: thrombus mass (grams/cm), vein wall inflammatory cells (cells per 5 high powered fields), active plasma plasminogen activator inhibitor-1 (PAI-1, ng/mL), vein wall P-selectin protein determination by ELISA (pg/mL), circulating plasma microparticles (MPs, MPs/200microL), MP tissue factor (TF) activity (pM), and in vivo MP re-injection experiments.

RESULTS

Thrombosed OLD mice had greater thrombus mass than YOUNG mice (389+/-18 vs. 336+/-14 gx10(-4)/cm, P<.05). OLD mice had decreased vein wall monocyte, lymphocyte, and total inflammatory cell populations versus YOUNG mice (P<.05). Vein wall P-selectin levels were greater in OLD thrombosed mice versus YOUNG (7306+/-938 vs. 3805+/-745pg/mL, P<.05). Active plasma PAI-1 concentrations were increased in OLD mice versus YOUNG thrombosed animals (20+/-4 vs. 8+/-2ng/mL, P<.05). OLD mice had significantly higher circulating leukocyte-derived MPs versus YOUNG mice (5817+/-850 vs. 2563+/-283 MPs/200muL PPP, P<.01). OLD mice had plasma MPs with increased TF activity versus YOUNG animals post-thrombosis (34+/-4 vs. 24+/-2 pM, P<.05). Finally, YOUNG recipient animals, whether re-injected with OLD or YOUNG donor MPs, had a significant increase in thrombus mass versus OLD recipient animals (P<.01).

CONCLUSION

Aging influenced several circulating and vein wall factors that decreased thrombus resolution in older animals compared to younger ones in our mouse thrombosis model.

Role of selectins and fibrinolysis in VTE

Venous thromboembolism (VTE) accounts for an estimated 900,000 cases of deep venous thrombosis (DVT) and pulmonary embolism (PE) yearly, resulting in approximately 300,000 deaths [1]. For the past 150 years, Virchow's triad has encompassed the elements of venous thrombogenesis, including stasis, changes in the vessel wall, and thrombogenic changes in the blood. However, in the early 1970s, through the work of Gwendylen Stewart, a relationship between thrombosis and inflammation was suggested. In this review, we will address the role of selectins and fibrinolysis in the process of venous thrombogenesis.

Leukocyte- and platelet-derived microparticles correlate with thrombus weight and tissue factor activity in an experimental mouse model of venous thrombosis

Microparticles (MP) are lipid vesicles from platelets, leukocytes and endothelial cells that are involved in early thrombogenesis. We evaluated a detailed time-course analysis of MPs on thrombogenesis and the associated tissue factor (TF) activity in wild-type, in gene-deleted for E- and P-selectins and with high levels of P-selectin expression after the initiation of venous thrombosis in mice. Inferior vena cava (IVC) ligation was performed on C57BL/6 mice (n = 191, 59 = wild-type [WT], 55 = gene-deleted for E- and P - selectins [knock-outs, EPKO] and 77 = elevated levels of soluble P-selectin, named Delta Cytoplasmic Tail (DeltaCT). Animals were euthanised at various time points to assess MP production, origin and thrombus weight. MPs were re-injected into separate mice at concentrations of 80,000 and 160,000 units, as well as from different ages. In addition, MPs from thrombosed animals were pooled and TF activity quantitated using a chromogenic assay. Thrombus weight correlated negatively with MPs derived from leukocytes, and positively with MPs derived from platelets for WT animals (p < 0.05), while MPs from platelets presented a positive correlation to thrombus weight in the WT and EPKO groups (p < 0.01). Total MPs correlated negatively with thrombus weight in the DeltaCT group (p < 0.05). MP re-injections led to greater thrombus weight, while older MP reinjections tended to form larger thrombus than younger. Finally, TF bearing MPs showed a significant correlation to MP concentrations (R = 0.99). In conclusion, MPs appear to be an important element in venous thrombogenesis.

Prophylactic P-selectin inhibition with PSI-421 promotes resolution of venous thrombosis without anticoagulation

P-selectin inhibition has been evaluated as a therapeutic for prevention and treatment of venous thrombosis. In this study, a novel oral small-molecule inhibitor of P-selectin, PSI-421, was evaluated in a baboon model of stasis induced deep vein thrombosis (DVT). Experimental groups included i) primates receiving a single oral dose of 1 mg/kg PSI-421 two days prior and continued six days after thrombosis (n = 3); ii) primates receiving a single daily subcutaneous dose of 0.57 mg/kg enoxaparin sodium two days prior and continued six days post thrombosis (n = 3); and iii) primates receiving no treatment (n = 3). PSI-421 treated primates had greater percent vein reopening and less vein wall inflammation than the enoxaparin and controls at day 6. Microparticle tissue factor activity (MPTFA) was significantly lower in the animals receiving PSI-421 immediately after thrombosis (T+6 hours day 0) suggesting lower potential for thrombogenesis in these animals. PSI-421 also reduced soluble P-selectin levels versus controls at T+6 hours day 0, day 2 and 6. Experimental animals in any group showed no adverse effects on coagulation. This study is the first to demonstrate a reduction in MPTFA associated with vein reopening and reduced vein inflammation due to oral P-selectin inhibition in a baboon model of DVT.

Mechanisms of Venous Thrombosis and Resolution

Venous thromboembolism is a significant health care problem in the US. In this review, the unique role of inflammation to the venous thrombotic process is emphasized as well as the potential role of abnormalities of fibrinolytic mechanisms to the thrombotic process. Inflammation influences not only thrombogenesis but also thrombus resolution and vein wall remodeling, and these interactions are also discussed. Knowledge of molecular and immunologic mechanisms for venous thrombosis and its resolution should allow for the future development of targeted therapies.

Gangrenous Clostridium perfringens infection and subsequent wound management in a rhesus macaque (Macaca mulatta)

A 10-y-old female rhesus macaque presented acutely with 3 large (diameter, greater than 4 cm), malodorous, ulcerogangrenous skin wounds on the left caudal thigh and calf. Limb radiographs revealed free gas infiltrating deep tissues, and histologic examination confirmed myonecrosis. Clostridium perfringens, Staphylococcus aureus, and Prevotella intermedia were isolated from the wounds. Antimicrobials, analgesics, and aggressive debridement of necrotic skin and muscle resulted in immediate clinical improvement of the primate. At 1 wk prior to presentation, the animal had received several intramuscular injections in close proximity to the site of infection. Repeated intramuscular injections through excrement-contaminated skin possibly contributed to the pathogenesis of infection. Continued therapy consisted of biweekly wound debridement and nonadherent bandage changes for 7 wk. The macaque regained full use of the affected leg and remains in good physical condition at our facility. Our management of this case led to improvements in training regarding intramuscular injection practices in our macaque colony. This case study is the first report of Clostridium perfringens myonecrosis in a laboratory nonhuman primate. We discuss various methodologies for the diagnosis and treatment of necrotizing clostridial infections.

Resolution of venous thrombosis using a novel oral small-molecule inhibitor of P-selectin (PSI-697) without anticoagulation

P-selectin inhibition has been shown to decrease thrombogenesis in multiple animal species. In this study, we show that a novel oral small-molecule inhibitor of P-selectin, PSI-697, promotes thrombus resolution and decreases inflammation in a baboon model of venous thrombosis. Experimental groups consisted of the following: 1) primates receiving a single oral dose of PSI-697 (30 mg/kg) daily starting three days pre-iliac vein balloon occlusion, and continued for six days; 2) primates receiving a single treatment dose of a low-molecular-weight-heparin (LMWH) (1.5 mg/kg) daily starting one day pre-iliac balloon occlusion, and continued for six days; and 3) primates receiving a single oral dose of a vehicle control daily starting three days pre-iliac vein balloon occlusion, and continued for six days. Animals receiving PSI-697, although thrombosed after balloon deflation, demonstrated greater than 80% vein lumen opening over time, with no opening (0%) for vehicle control (p < 0.01). LMWH opening evident after balloon deflation slightly deteriorated over time compared to PSI-697. PSI-697 therapy also significantly decreased vein wall inflammation determined by magnetic resonance venography (MRV). Importantly, this beneficial opening occurred without measured anticoagulation. Animals receiving PSI-697 demonstrated significantly increased plasma D-dimer levels versus LMWH and control animals six hours post thrombus induction (p < 0.01). This study is the first to demonstrate the effectiveness of oral P-selectin inhibition to modify venous thrombogenesis, increase vein lumen opening, and decrease inflammation in a large animal model.