1D-¹H-nuclear magnetic resonance metabolomics reveals age-related changes in metabolites associated with experimental venous thrombosis

OBJECTIVE

Age is a significant risk factor for the development of venous thrombosis (VT), but the mechanism(s) that underlie this risk remain(s) undefined and poorly understood. Aging is known to adversely influence inflammation and affect metabolism. Untargeted metabolomics permits an agnostic assessment of the physiological landscape and lends insight into the mechanistic underpinnings of clinical phenotypes. The objective of this exploratory study was to test the feasibility of a metabolomics approach for identifying potential metabolic mechanisms of age-related VT.

METHODS

We subjected whole blood samples collected from young and old nonthrombosed controls and VT mice 2 days after thrombus induction using the electrolytic inferior vena cava, to a methanol:chloroform extraction and assayed the resulting aqueous fractions using 1D-(1)H- nuclear magnetic resonance. Normalized mouse metabolite data were compared across groups using analysis of variance (ANOVA) with Holm-Sidak post-testing. In addition, associations between metabolite concentrations and parameters of thrombosis such as thrombus and vein wall weights, and markers of inflammation, vein wall P- and E-selectin levels, were assessed using linear regression. The relatedness of the found significant metabolites was visually assessed using a bioinformatics tool, Metscape, which generates compound-reaction-enzyme-gene networks to aid in the interpretation of metabolomics data.

RESULTS

Old mice with VT had a greater mean vein wall weight compared with young mice with VT (P < .05). Clot weight differences between old and young mice followed the same trend as vein wall weight (0.011 ± 0.04 g vs 0.008 ± 0.003 g; P = not significant). Glutamine (ANOVA, P < .01), proline (ANOVA, P < .01), and phenylalanine (ANOVA, P < .05) levels were increased in old VT mice compared with age-matched controls and young VT mice. Betaine and/or trimethylamine N-oxide levels were increased in aged mice compared with young animals. Vein wall weight was strongly associated with glutamine (P < .05), and phenylalanine (P < .01) concentrations and there was a trend toward an association with proline (P = .09) concentration. Vein wall P-selectin, but not E-selectin levels, were increased in old VT mice and were associated with the three found metabolites of age-related VT. Collectively, with the addition of glutamate, these metabolites form a single compound-reaction-enzyme-gene network that was generated by Metscape.

CONCLUSIONS

We used 1D-(1)H-nuclear magnetic resonance-metabolite profiling to identify, for the first time, in an experimental model, three potential metabolites, glutamine, phenylalanine, and proline, associated with age-related VT. These metabolites are metabolically related and their levels are associated with vein wall weight and P-selectin concentrations. In aggregate, these findings provide a "roadmap" of pathways that could be interrogated in future studies, which could include provocation of the glutamine, phenylalanine, and proline pathways in the vein wall. This study introduces metabolomics as a new approach to furthering knowledge about the mechanisms of age-related VT.

Abstract 24: Resolvin D2 Reduces Thrombus Burden and Attenuates Inflammatory Signaling Pathways in a Murine Model of Venous Thrombosis

Background: Specialized pro-resolving lipid mediators (SPM) derived from polyunsaturated fatty acids, such as Resolvin D2 (RvD2), play a critical role in the resolution of acute inflammation. In recent years, total organic synthesis of SPM have enabled investigation of their bioactivity in-vivo. It is known that the effects of RvD2 include limited neutrophil influx in-vivo, reduced neutrophil transmigration and counter-regulation of cytokines such as tumor necrosis factor-α TNF-α in mice. However, SPMs have not been studied in the context of experimental venous thrombosis (VT).

Methods: Mice C57Bl/6, 10 week-old, 25grams. Groups: Control non-VT mice; VT-control-vehicle; VT-RvD2; Flow model: Electrolytic IVC model. Intra-peritoneal injection was used for RvD2 and vehicle administration 4 hours after surgery. Harvest was performed 2 days after surgery, acute VT. Thrombus weight, qRT-PCR for inflammatory cytokines panel and subsets of white blood cell (WBC) counts were performed at the site of thrombosis histologically.

Results (Figure 1): We observed that RvD2 significantly reduced thrombus size when compared to vehicle controls (17.9mg±2.1mg vs. 4.5mg±0.8mg). The vein wall cytokine profile demonstrated a significant gene down-regulation of IL-6, CCL2, and TNF-a. In addition, the inflammatory cell counts showed reduction in all white cells subsets. No bleeding complications were observed.

Conclusions: For the first time we have demonstrated that RvD2 reduces VT formation. The decreased thrombogenesis was accompanied by a decrease in WBC and proinflammatory cytokines. We demonstrated that RvD2 is a potent anti-inflammatory agent that reduced WBC and attenuated cytokines in the context of experimental VT. Further investigation of RvD2 in VT treatment and prophylaxis appears warranted.

Inferior vena cava branch variations in C57BL/6 mice have an impact on thrombus size in an IVC ligation (stasis) model

BACKGROUND

Animal models of venous thrombosis (VT) are critical tools for those investigating the VT mechanism. Recently, inferior vena cava (IVC) branches have been subject to debate, causing controversy in the field.

OBJECTIVES

To understand how the variability of IVC branches, in commonly used C57BL/6 mice, have an impact on thrombus formation in the IVC ligation model.

METHODS

C57BL/6 male mice (n = 46), 20-25 g, were subjected to the IVC ligation model with various interruptions of the IVC branches. Control animals (n = 50) had all branches interrupted. Two days after IVC ligation, thrombus weight (TW), as a parameter of thrombus size, was assessed.

RESULTS

We found four different anatomical patterns. Side branches were more prevalent on the mouse's right side (34%) compared with the left (20%). In mice where side branches were absent (21%), back branches appeared larger. Also, 25% of mice had both side branches. Controls that had all IVC branches interrupted had the most consistent and largest TW (32.6 mg to 34.7 mg) while groups that had no back branches interrupted had the smallest TW (3.6-9.7 mg), a 4 to 9-fold decrease. All groups with open back branches had significantly smaller TW (P < 0.05) than controls.

CONCLUSIONS

Variations in TW were observed based on different branch interruption patterns, compared with the fully ligated controls. Having two back branches was the most consistent anatomy and open back branches had the largest negative impact on thrombus size. This work confirms that the IVC branches significantly affect thrombus burden in C57BL/6 mice and further studies should be conducted in order to standardize this and other animal models of VT.

Low-molecular-weight heparin modulates vein wall fibrotic response in a plasminogen activator inhibitor 1-dependent manner

BACKGROUND

Treatment with low-molecular-weight heparin (LMWH) favorably alters the vein wall response to deep venous thrombosis (DVT), although the mechanisms remain unclear. Previous studies have suggested that LMWH alters the levels of circulating plasminogen activator inhibitor 1 (PAI-1), a known mediator of fibrosis, and may improve endogenous fibrinolysis. We hypothesized that LMWH favorably alters the vein wall response by binding of PAI-1 and acceleration of fibrinolysis.

METHODS

Wild-type and PAI-1 ^-/- mice underwent treatment with LMWH after induction of occlusive DVT. Vein wall and plasma were harvested and analyzed by enzyme-linked immunosorbent assay, zymography, real-time polymerase chain reaction, and immunohistochemistry.

RESULTS

Wild-type mice treated with LMWH exhibited diminished vein wall fibrosis (0.6 ± 0.6 vs 1.4 ± 0.2; P < .01; n = 5) and elevation of circulating PAI-1 (1776 ± 342 vs 567 ± 104 ρg/mL; P < .01; n = 5) compared with untreated controls after occlusive DVT. PAI-1^-/- mice treated with LMWH were not similarly protected from fibrosis, despite improved thrombus resolution. Treatment with LMWH was associated with decreased intrathrombus interleukin-lβ (68.6 ± 31.0 vs 223.4 ± 28.9 ρg/mg total protein; P < .01; n = 5) but did not alter inflammatory cell recruitment to the vein wall. PAI-1 ^-/- mice exhibited significantly elevated intrathrombus (257.2 ± 51.5 vs 4.3 ± 3.8 ρg/mg total protein; n = 5) and vein wall interleukin-13 (187.2 ± 57.6 vs 9.9 ± 1.1 ρg/mg total protein; P < .05; n = 5) as well as vein wall F4/80 positively staining monocytes (53 ± 11 vs 16 ± 2 cells/5 high-power fields; P < .05; n = 4).

CONCLUSIONS

LMWH did not accelerate venous thrombosis resolution but did protect against vein wall fibrosis in a PAI-1-dependent manner in an occlusive DVT model. Lack of PAI-1 correlated with accelerated venous thrombosis resolution but no protection from fibrosis. PAI-1 inhibition as a treatment strategy for DVT is likely to accelerate clearance of the thrombus but may come at the expense of increased vein wall fibrosis.

CLINICAL RELEVANCE

The pathophysiologic mechanism of post-thrombotic syndrome is not well understood clinically or experimentally. In this study, we evaluated the effect of the prominent fibrinolytic mechanism, plasminogen activator inhibitor 1 (PAI-1), and low-molecular-weight heparin (LMWH) on vein wall injury after thrombosis. We show here that LMWH is protective from vein wall fibrosis, but this is abrogated in PAI-1-deleted mice. This is also correlated with monocyte vein wall influx. These data support the clinical observation that LMWH may be protective from post-thrombotic vein wall injury in a PAI-1-dependent manner.

Plasminogen activator-1 overexpression decreases experimental postthrombotic vein wall fibrosis by a non-vitronectin-dependent mechanism

BACKGROUND

Factors associated with postthrombotic syndrome are known clinically, but the underlying cellular processes at the vein wall are not well delineated. Prior work suggests that vein wall damage does not correlate with thrombus resolution but rather with plasminogen activator-1 (PAI-1) and matrix metalloproteinase (MMP) activity.

OBJECTIVE

We hypothesized that PAI-1 would confer post venous thrombosis (VT) vein wall protection via a vitronectin (Vn)-dependent mechanism.

METHODS

A stasis model of VT was used with harvest over 2 weeks, in wild-type, Vn(-/-) , and PAI-1-overexpressing mice (PAI-1 Tg).

RESULTS

PAI-1 Tg mice had larger VT at 6 and 14 days, compared to controls, but Vn(-/-) mice had no alteration of VT resolution. Gene deletion of Vn resulted in an increase in, rather than the expected decrease in, circulating PAI-1 activity. While both Vn(-/-) and PAI-1 Tg had attenuated intimal fibrosis, PAI-1 Tg had significantly less vein wall collagen and a compensatory increase in collagen III gene expression. Both Vn(-/-) and PAI-1 Tg vein wall had less monocyte chemotactic factor-1 and fewer macrophages (F4/80), with significantly less MMP-2 activity and decreased TIMP-1 antigen. Ex vivo assessment of transforming growth factor β-mediated fibrotic response showed that PAI-1 Tg vein walls had increased profibrotic gene expression (collagens I and III, MMP-2, and α-smooth muscle actin) compared with controls, opposite of the in vivo response.

CONCLUSIONS

The absence of Vn increases circulating PAI-1, which positively modulates vein wall fibrosis in a dose-dependent manner. Translationally, PAI-1 elevation may decrease vein wall damage after deep vein thrombosis, perhaps by decreasing macrophage-mediated activities.

The electrolytic inferior vena cava model (EIM) to study thrombogenesis and thrombus resolution with continuous blood flow in the mouse

Previously, we presented the electrolytic inferior vena cava (IVC) model (EIM) during acute venous thrombosis (VT). Here, we present our evaluation of the EIM for chronic VT time points in order to determine whether this model allows for the study of thrombus resolution. C57BL/6 mice (n=191) were utilised. In this model a copper-wire, inserted into a 25-gauge needle, is placed in the distal IVC and another subcutaneously. An electrical current (250 μAmp/15 minutes) activates the endothelial cells, inducing thrombogenesis. Ultrasound, thrombus weight (TW), vein wall leukocyte counts, vein wall thickness/fibrosis scoring, thrombus area and soluble P-selectin (sP-sel) were performed at baseline, days 1, 2, 4, 6, 9, 11 and 14, post EIM. A correlation between TW and sP-sel was also determined. A thrombus formed in each mouse undergoing EIM. Blood flow was documented by ultrasound at all time points. IVC thrombus size increased up to day 2 and then decreased over time, as shown by ultrasound, TW, and sP-sel levels. TW and sP-sel showed a strong positive correlation (r=0.48, p<0.0002). Vein wall neutrophils were the most common cell type present in acute VT (up to day 2) with monocytes becoming the most prevalent in chronic VT (from day 6 to day 14). Thrombus resolution was demonstrated by ultrasound, TW and thrombus area. In conclusion, the EIM produces a non-occlusive and consistent IVC thrombus, in the presence of constant blood flow, allowing for the study of VT at both acute and chronic time points. Thrombus resolution was demonstrated by all modalities utilised in this study.

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.

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.

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.

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.

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.

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.

Decreased venous thrombosis with an oral inhibitor of P selectin

BACKGROUND

P-selectin inhibition with protein therapeutics such as antibodies or soluble ligands given intravenously can decrease thrombosis in a mouse ligation model of venous thrombosis. In this study, we hypothesized that oral inhibition of P selectin with a novel oral nonprotein inhibitor (PSI-697) would decrease thrombosis and circulating microparticle populations. This study evaluated the effects on thrombosis and circulating microparticle populations in this murine venous thrombosis model.

METHODS

Mice underwent inferior vena cava ligation to induce thrombosis. Mice with high circulating level of P selectin, Delta Cytoplasmic Tail (CT), mice gene-deleted for both E- and P-selectin knockout (EPKO), and wild-type C57BL/6 mice (WT) were studied without and with administration of PSI-697 in food (100 mg/kg daily) from 2 days before thrombosis until the end of the study. Animals were killed 2 and 6 days later. Evaluations included thrombus weight (TW), vein wall morphometrics, microparticle quantification by using fluorescence-activated cell sorter analysis, and vein wall enzyme-linked immunosorbent assays for interleukin (IL)-10, P selectin, and monocyte chemotactic protein 1.

RESULTS

PSI-697 significantly decreased TW in WT and CT mice, with a treated vs nontreated TW of 132 +/- 24 vs 228 +/- 29 x 10(-4) g (P = .014) and 166 +/- 19 vs 281 +/- 16 x 10(-4) g (P = .001), respectively. At day 6, the effect was significant only in the CT group (P < .05). Drug therapy at day 2 significantly increased vein wall monocytes in WT mice and increased monocytes and total inflammatory cells in CT animals. A significant decrease in neutrophils and total inflammatory cells was seen in EPKO mice at day 2 with therapy. Therapy significantly increased platelet-derived microparticles and total microparticles in CT mice on day 2. Changes in treated WT and treated EPKO animals were not significant compared with respective vehicle treatments at day 2. On day 6, therapy significantly decreased total microparticles in EPKO animals. Vein wall expression of IL-10 increased in all groups with therapy at day 2 (n = 18) and was significantly increased in WT (2687.5 +/- 903 pg/mL vs 636 +/- 108 pg/mL total protein; P = .038) and CT (2078 +/- 295 pg/mL vs 432 +/- 62 pg/mL total protein; P = .001) mice. Therapy significantly decreased vein wall P selectin, monocyte chemotactic protein 1, and IL-10 levels at day 6.

CONCLUSIONS

PSI-697 decreased thrombosis. P-selectin inhibition allowed vein wall inflammatory cell extravasation in this model of complete ligation. Circulating microparticles (platelet-derived microparticles and total microparticles) increased with P-selectin inhibition, possibly because of decreased consumption into the thrombus. In summary, the oral administration of an inhibitor to P selectin provides significant TW reduction.

CLINICAL RELEVANCE

Deep venous thrombosis is a significant national health problem in the general population. The average annual incidence of deep venous thrombosis is approximately 250,000 cases per year. The selectin family of adhesion molecules is thought to be largely responsible for the initial attachment and rolling of leukocytes on stimulated vascular endothelium. Recent studies have explored the possible therapeutic implications of P-selectin inhibition to modulate venous thrombosis. For example, prophylactic dosing of a recombinant P-selectin ligand decreases venous thrombosis in a dose-dependent fashion in both feline and nonhuman primate animal models. Additionally, treatment of 2-day iliac thrombi with a recombinant protein, P-selectin inhibitor, significantly improves vein reopening in nonhuman primates. It is interesting to note that P-selectin inhibition decreases thrombosis without adverse anticoagulation. On the basis of the results from these previous studies, the use of P-selectin antagonism is a logical therapeutic approach to treat venous thrombosis. All inhibitors developed to date are either proteins or small molecules with low oral bioavailability that require intravenous or subcutaneous injection. This study evaluates, for the first time, a novel orally bioavailable inhibitor of P-selectin (PSI-697).

Macrovascular thrombosis is driven by tissue factor derived primarily from the blood vessel wall

Leukocytes and leukocyte-derived microparticles contain low levels of tissue factor (TF) and incorporate into forming thrombi. Although this circulating pool of TF has been proposed to play a key role in thrombosis, its functional significance relative to that of vascular wall TF is poorly defined. We tested the hypothesis that leukocyte-derived TF contributes to thrombus formation in vivo. Compared to wild-type mice, mice with severe TF deficiency (ie, TF–/–, hTF-Tg+, or “low-TF”) demonstrated markedly impaired thrombus formation after carotid artery injury or inferior vena cava ligation. A bone marrow transplantation strategy was used to modulate levels of leukocyte-derived TF. Transplantation of low-TF marrow into wild-type mice did not suppress arterial or venous thrombus formation. Similarly, transplantation of wild-type marrow into low-TF mice did not accelerate thrombosis. In vitro analyses revealed that TF activity in the blood was very low and was markedly exceeded by that present in the vessel wall. Therefore, our results suggest that thrombus formation in the arterial and venous macrovasculature is driven primarily by TF derived from the blood vessel wall as opposed to leukocytes.

P-selectin and leukocyte microparticles are associated with venous thrombogenesis

OBJECTIVES

P-selectin inhibition has been found to limit venous thrombosis. We hypothesize that elevated levels of P-selectin will amplify thrombosis, mediated by procoagulant microparticles (MPs).

METHODS

Male mice (Mus musculus, n659), 20 to 25 grams, underwent IVC ligation to induce thrombosis. Groups consisted of wild type (WT) C57BL/6 controls, mice with high circulating levels of soluble P-selectin (CT), P-selectin gene-interrupted knockout mice (PKO), and E- and P-selectin gene-interrupted mice (EPKO). Additional groups were used to evaluate the ability of a P-sel antagonist (rPSGL-Ig) and an antibody directed against PSGL-1 to downregulate the effects of P-sel in CT mice and WT mice administered soluble P-sel at time of thrombosis. Animals were sacrificed on days 2 and 6 after IVC ligation. Thrombus mass (TM), vein wall morphometrics, and serum leukocyte/platelet microparticles (MPs) were evaluated by means of double-stained fluorescence-activated cell scanning analysis, and soluble P- and E-sel protein determination by ELISA.

RESULTS

At days 2 and 6 in phase I of the experiment, significant differences (P <.01) in TM were noted between groups, with CT animals having the largest thrombi (50% and 57% increase in TM compared to WT at days 2 and 6) while EPKO mice had the smallest thrombi. Statistically, greater levels of neutrophils and total inflammatory cells were noted in the vein walls of CT animals at day 2 compared with WT and PKO animals. A significant difference was noted between CT and EPKO for neutrophils, monocytes, and total inflammatory cells, also at day 2. At day 6, the only statistically significant difference was found for monocytes, with a higher number in the CT animals than in WT animals. The evaluation of MPs revealed that the CT mice had a mixed leukocyte (MAC-1) and platelet (CD41) MP population that was also present in WT and PKO mice on day 2 and day 6. EPKO mice revealed a primarily platelet-derived MP population. Of interest, the CT mice with the highest TM showed a high amount of mean channel fluorescence for MAC-1 (phycoerythrin) antibody, indicative of leukocyte MPs. CT mice revealed statistically higher levels of soluble P-selectin at days 2 and 6. In phase 2, an antibody directed against PSGL-1 was more effective than rPSGL-Ig in decreasing TM and limiting leukocyte-derived MP fluorescence.

CONCLUSIONS

This study demonstrates that high circulating levels of P-selectin are associated with increased thrombosis, whereas a lack of P-selectin and E-selectin is associated with a lessening of thrombosis. Additionally, leukocyte MPs are associated with venous thrombus formation. These data suggest the importance of selectins to venous thrombogenesis and show that P-selectin and leukocyte-derived MPs should be good targets to limit venous thrombus formation.

P-selectin inhibition decreases post-thrombotic vein wall fibrosis in a rat model

BACKGROUND

Post-deep vein thrombosis (DVT) venous insufficiency is a vexing problem despite effective anticoagulation, and is characterized by vein wall fibrosis. This study tested the hypothesis that P-selectin inhibition would decrease post-thrombotic vein wall fibrosis and associated profibrotic mediators.

METHODS

A rat stasis model of DVT was used to produce a 2-day-old DVT. Rats then received either intravenous saline (control), rPSGL-Ig (4 mg/kg) once, or daily subcutaneous low molecular weight heparin (LMWH) (0.5 mg/kg). Inferior vena cava wall was harvested 7 days after treatment and processed for thrombus size; leukocyte content; profibrotic mediators by enzyme-linked immunosorbent assay; collagen I and III mRNA expression by semiquantitative real-time polymerase chain reaction; and for collagen protein.

RESULTS

Thrombus mass and leukocyte counts were similar between the groups. Treatment with rPSGL-Ig and LMWH resulted in less vein wall collagen (P <.05). rPSGL-Ig treatment (and a similar trend for LMWH) was associated with decreased profibrotic mediators, including less IL-13, MCP-1, bFGH, and transforming growth factor-beta (P <.05). Collagen III gene expression, but not collagen I gene expression, was increased with LMWH treatment (P <.05).

CONCLUSIONS

P-selectin inhibition with rPSGL-Ig or LMWH decreases post-DVT vein wall fibrosis, and is associated with decreased vein wall profibrotic mediators. This effect is independent of thrombus mass and vein wall leukocytes.

Cellular IL-10 is more effective than viral IL-10 in decreasing venous thrombosis

BACKGROUND

Systemic administration of cellular interleukin-10 (cIL-10) and gene transfection of viral interleukin-10 (vIL-10) at thrombus induction decreases vein wall inflammation. Only cIL-10, despite sharing an 84% amino acid sequence homology with vIL-10, decreases thrombosis through mechanisms yet to be determined.

METHODS

C57BL/6 mice (Mus musculus, n99) were studied. Inferior vena caval thrombosis was created by inferior vena caval ligation and the animals were sacrificed and evaluated at days 2 and 6 after ligation. At thrombus induction groups received intravenous 0.25 microg of cIL-10, 0.25 microg of vIL-10, or saline (untreated controls). Evaluations included thrombus mass and vein wall leukocyte counts, protein levels, and reverse-transcription polymerase chain reaction mRNA levels of P- and E-selectin, monocyte chemotactic protein-1, and IL-10. Groups were compared by analysis of variance and t tests.

RESULTS

Less thrombus was noted at both days 2 and 6 in animals treated with cIL-10. At day 2 only, vein wall leukocyte counts revealed a significant decrease in neutrophils in cIL-10 animals versus controls, with no significant differences for vIL-10 animals. In cIL-10-treated animals, P-selectin protein levels were decreased at day 6, along with a decreased thrombus mass, without significant differences in E-selectin, monocyte chemotactic protein-1, or IL-10 protein levels. vIL-10 treated animals showed increased E-selectin mRNA and thrombus mass versus controls on day 6.

CONCLUSIONS

cIL-10 is more antithrombotic/anti-inflammatory than vIL-10. This may be the result of cIL-10 decreasing P-selectin protein expression and vIL-10 increasing E-selectin mRNA levels.

Decrease in fibrin content of venous thrombi in selectin-deficient mice

The purpose of this study was to quantify the fibrin content of thrombi produced in a mouse model of venous thrombosis and correlate this to thrombus mass. The role of P-selectin, E-selectin, and IL-10 on thrombus fibrin content was analyzed using knockout (KO) mice. Five groups of mice were evaluated: control (N = 10), P-selectin KO (N = 7), E-selectin KO (N = 5), combined E-/P-selectin KO (N = 12), and IL-10 KO (N = 10). Venous thrombosis was induced by ligation of the infrarenal IVC. Mice were sacrificed on postoperative days (POD) 2 and 6. Thrombus mass was calculated. Sections of IVC were stained with an antibody that cross reacts with mouse fibrin. The distribution of RGB color pixels was generated from digitized micrographs of the thrombus of each animal. The mean pixel value for each group was compiled and analyzed using 2-way ANOVA. Mean pixel value per group was correlated with the mean thrombus mass per group. Color analysis demonstrated significant decreases in the analyzed fibrin content on POD-2 between the control vs E-/P-selectin KO (P < 0.05) and control vs IL-10 KO (P < 0.05) groups. In addition, significantly less fibrin staining was noted on POD-6 between the control vs E-selectin KO (P = 0.03), control vs P-selectin KO (P = 0.01), and control vs E-/P-selectin KO (P < 0.01). There was a strong overall correlation between the mean pixel value for each group and the thrombus mass (R = 0.964; P < 0.01). This study demonstrates a difference in fibrin content of thrombi produced in animals deficient in E-selectin, P-selectin, and IL-10, supporting their importance in thrombus amplification, fibrin formation, and the mass of thrombus formed.

P-selectin inhibition enhances thrombus resolution and decreases vein wall fibrosis in a rat model

PURPOSE

The purpose of this study was to compare the efficacy of P-selectin inhibition with standard anticoagulant and thrombolytic therapy in a rodent model of established deep vein thrombosis (DVT).

METHODS

Rats underwent temporary inferior vena cava (IVC) ligation for 2 days to create a stasis-induced thrombosis. On day 2, the animals had the IVC ligature removed and received either recombinant P-selectin glycoprotein ligand-Ig (rPSGL-Ig; 4 mg/kg) intravenously, low-molecular weight heparin (LMWH; 450 IU/kg) subcutaneously, tissue plasminogen activator (tPA; 0.5 mg/kg) intravenously, combination rPSGL-Ig plus tPA, or saline vehicle. IVC segments were harvested from rats at 4 (n = 8) and 7 (n = 3) days after treatment. All treatments were given as a single dose except for daily LMWH. Evaluation included contrast venography with computer image analysis, thrombus weight/length (mass), vein wall leukocyte counts, cytokine and tissue factor analysis with enzyme-linked immunosorbent assay, and (ED1) monocyte immunohistochemical staining. Collagen was estimated with a quantitative assay.

RESULTS

Contrast venography revealed that rats with both rPSGL-Ig and tPA treatment had significantly smaller thrombi as compared with controls at day 7 (0.34 +/- 0.07 cm(2) and 0.34 +/- 0.05 cm(2) versus 0.68 +/- 0.13 cm(2); P <.05). LMWH and tPA groups had significantly decreased thrombus mass at harvest compared with controls on day 4 (0.06 +/- 0.009 g/cm and 0.08 +/- 0.01 g/cm versus 0.1 +/- 0.005 g/cm; P <.05), and rPSGL-Ig showed a similar trend (P =.072). Vein wall, but not thrombus, monocytes were more numerous in those rats receiving rPSGL-Ig versus controls at day 4 (30 +/- 4 cells/5 high power fields [HPFs] versus 19 +/- 2 cells/5 HPFs; P <.05) and at day 7 (32 +/- 2 cells/5 HPFs versus 20 +/- 3 cells/5 HPFs; P <.05). rPSGL-Ig treatment was associated with significantly reduced vein wall collagen at day 7 versus controls (1.3 +/- 0.6 pg/mg versus 3.7 +/- 0.5 pg/mg; P <.05) and a trend toward lower tissue factor levels.

CONCLUSION

rPSGL-Ig, LMWH, and tPA showed equal DVT resolution efficacy over 7 days. However, only rPSGL-Ig was associated with a decrease in vein wall fibrosis, suggesting that purely accelerating DVT resolution may not decrease long-term vein scarring.