Mouse models of focal arterial and venous thrombosis

Prehospital coagulation measurement by a portable blood analyzer in a helicopter emergency medical service (HEMS)

In helicopter emergency medical services, HEMS, coagulopathy presents both in trauma (e.g. consumption of coagulation factors) and non-trauma cases (e.g. anticoagulant use). Therefore, in HEMS coagulation measurements appear promising and Prothrombin Time (PT) and derived INR are attractive variables herein. We tested the feasibility of prehospital PT/INR coagulation measurements in HEMS. This study was performed at the Dutch HEMS, using a portable blood analyzer (i-Stat®1, Abbott). PT/INR measurements were performed on (hemodiluted) author's blood, and both trauma- and non-trauma HEMS patients. Device-related benefits of the i-Stat PT/INR system were portability, speed and ease of handling. Limitations included a rather narrow operational temperature range (16-30 °C). PT/INR measurements (n = 15) were performed on hemodiluted blood, and both trauma and non-trauma patients. The PT/INR results confirmed effects of hemodilution and anticoagulation, however, most measurement results were in the normal INR-range (0.9-1.2). We conclude that prehospital PT/INR measurements, although with limitations, are feasible in HEMS operations.

Depletion of CD4 and CD8 Positive T Cells Impairs Venous Thrombus Resolution in Mice

Resolution of deep venous thrombosis involves coordinated inflammatory processes. T cells regulate inflammation in vivo and modulate vascular remodeling in other settings, but their role in venous thrombus resolution remains undefined. To determine the role of T cells in venous thrombus resolution in vivo, stasis induced thrombi were created by vena cava ligation in outbred CD-1 mice. CD4 and CD8 positive T cells, as determined by flow cytometry, were present in thrombi both during thrombus formation and resolution. Depletion of the CD4 and CD8 positive T cells by antibody treatment selectively impaired thrombus resolution compared to animals treated with isotype control antibodies, without an effect on venous thrombus formation. Quantitation of intra-thrombus macrophage numbers, fibrinolytic marker expression, and gelatinolytic activity by zymography revealed that T cell depletion decreased the number of macrophages, reduced the expression of fibrinolytic marker urokinase plasminogen activator (uPA), and decreased the activity of matrix metalloprotinease-9 (MMP-9). These data implicate CD4 and CD8 positive T cells in functionally contributing to venous thrombus resolution, thus representing a potential therapeutic target, but also underscoring potential risks involved in T cell depletion used clinically for solid organ and hematopoietic transplantation procedures.

Fibrinolysis and Inflammation in Venous Thrombus Resolution

Clinical observations and accumulating laboratory evidence support a complex interplay between coagulation, inflammation, innate immunity and fibrinolysis in venous thromboembolism (VTE). VTE, which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), and the subsequent complications of post-thrombotic syndrome (PTS), are significant causes of morbidity and mortality in patients. Clinical risk factors for VTE include cancer, major trauma, surgery, sepsis, inflammatory bowel disease, paralysis, prolonged periods of immobility, and aging. Abnormalities in venous blood flow or stasis initiates the activation of endothelial cells, and in concert with platelets, neutrophils and monocytes, propagates VTE in an intact vein. In addition, inflammatory cells play crucial roles in thrombus recanalization and restoration of blood flow via fibrinolysis and vascular remodeling. Faster resolution of the thrombus is key for improved disease prognosis. While in the clinical setting, anticoagulation therapy is successful in preventing propagation of venous thrombi, current therapies are not designed to inhibit inflammation, which can lead to the development of PTS. Animal models of DVT have provided many insights into the molecular and cellular mechanisms involved in the formation, propagation, and resolution of venous thrombi as well as the roles of key components of the fibrinolytic system in these processes. Here, we review the recent advances in our understanding of fibrinolysis and inflammation in the resolution of VTE.

Antiplatelet Aggregation and Antithrombosis Efficiency of Peptides in the Snake Venom of Deinagkistrodon acutus: Isolation, Identification, and Evaluation

Two peptides of Pt-A (Glu-Asn-Trp 429 Da) and Pt-B (Glu-Gln-Trp 443 Da) were isolated from venom liquor of Deinagkistrodon acutus. Their antiplatelet aggregation effects were evaluated with platelet-rich human plasma in vitro; the respective IC₅₀ of Pt-A and Pt-B was 66 μM and 203 μM. Both peptides exhibited protection effects on ADP-induced paralysis in mice. After ADP administration, the paralysis time of different concentration of Pt-A and Pt-B lasted as the following: 80 mg/kg Pt-B (152.8 ± 57.8 s) < 40 mg/kg Pt-A (163.5 ± 59.8 s) < 20 mg/kg Pt-A (253.5 ± 74.5 s) < 4 mg/kg clopidogrel (a positive control, 254.5 ± 41.97 s) < 40 mg/kg Pt-B (400.8 ± 35.9 s) < 10 mg/kg Pt-A (422.8 ± 55.4 s), all of which were statistically shorter than the saline treatment (666 ± 28 s). Pulmonary tissue biopsy confirmed that Pt-A and Pt-B prevented the formation of thrombi in the lung. Unlike ADP injection alone, which caused significant reduction of peripheral platelet count, Pt-A treatment prevented the drop of peripheral platelet counts; interestingly, Pt-B could not, even though the same amount of Pt-B also showed protection effects on ADP-induced paralysis and thrombosis. More importantly, intravenous injection of Pt-A and Pt-B did not significantly increase the hemorrhage risks as clopidogrel.

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.

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.

Evaluation of plaque stability of advanced atherosclerotic lesions in apo E-deficient mice after treatment with the oral factor Xa inhibitor rivaroxaban

Aim. Thrombin not only plays a central role in thrombus formation and platelet activation, but also in induction of inflammatory processes. Activated factor X (FXa) is traditionally known as an important player in the coagulation cascade responsible for thrombin generation. We assessed the hypothesis that rivaroxaban, a direct FXa inhibitor, attenuates plaque progression and promotes stability of advanced atherosclerotic lesions in an in vivo model. Methods and Results. Rivaroxaban (1 or 5 mg/kg body weight/day) or standard chow diet was administered for 26 weeks to apolipoprotein E-deficient mice (n = 20 per group) with already established atherosclerotic lesions. There was a nonsignificant reduction of lesion progression in the high-concentration group, compared to control mice. FXa inhibition with 5 mg Rivaroxaban/kg/day resulted in increased thickness of the protective fibrous caps (12.3 ± 3.8 μm versus 10.1 ± 2.7 μm; P < .05), as well as in fewer medial erosions and fewer lateral xanthomas, indicating plaque stabilizing properties. Real time-PCR from thoracic aortas revealed that rivaroxaban (5 mg/kg/day) treatment reduced mRNA expression of inflammatory mediators, such of IL-6, TNF-α, MCP-1, and Egr-1 (P < .05). Conclusions. Chronic administration of rivaroxaban does not affect lesion progression but downregulates expression of inflammatory mediators and promotes lesion stability in apolipoprotein E-deficient mice.

Atherosclerosis and thrombosis: insights from large animal models

Atherosclerosis and its thrombotic complications are responsible for remarkably high numbers of deaths. The combination of in vitro, ex vivo, and in vivo experimental approaches has largely contributed to a better understanding of the mechanisms underlying the atherothrombotic process. Indeed, different animal models have been implemented in atherosclerosis and thrombosis research in order to provide new insights into the mechanisms that have already been outlined in isolated cells and protein studies. Yet, although no model completely mimics the human pathology, large animal models have demonstrated better suitability for translation to humans. Indeed, direct translation from mice to humans should be taken with caution because of the well-reported species-related differences. This paper provides an overview of the available atherothrombotic-like animal models, with a particular focus on large animal models of thrombosis and atherosclerosis, and examines their applicability for translational research purposes as well as highlights species-related differences with humans.

High-resolution magnetic resonance angiography in the mouse using a nanoparticle blood-pool contrast agent

High-resolution magnetic resonance angiography is already a useful tool for studying mouse models of human disease. Magnetic resonance angiography in the mouse is typically performed using time-of-flight contrast. In this work, a new long-circulating blood-pool contrast agent-a liposomal nanoparticle with surface-conjugated gadolinium (SC-Gd liposomes)-was evaluated for use in mouse neurovascular magnetic resonance angiography. A total of 12 mice were imaged. Scan parameters were optimized for both time-of-flight and SC-Gd contrast. Compared to time-of-flight contrast, SC-Gd liposomes (0.08 mmol/kg) enabled improved small-vessel contrast-to-noise ratio, larger field of view, shorter scan time, and imaging of venous structures. For a limited field of view, time-of-flight and SC-Gd were not significantly different; however, SC-Gd provided better contrast-to-noise ratio when the field of view encompassed the whole brain (P < 0.001) or the whole neurovascular axis (P < 0.001). SC-Gd allowed acquisition of high-resolution magnetic resonance angiography (52 x 52 x 100 micrometer(3) or 0.27 nL), with 123% higher (P < 0.001) contrast-to-noise ratio in comparable scan time ( approximately 45 min). Alternatively, SC-Gd liposomes could be used to acquire high-resolution magnetic resonance angiography (0.27 nL) with 32% higher contrast-to-noise ratio (P < 0.001) in 75% shorter scan time (12 min).

In vivo veritas: Thrombosis mechanisms in animal models

Experimental models have enhanced our understanding of atherothrombosis pathophysiology and have played a major role in the search for adequate therapeutic interventions. Various animal models have been developed to simulate thrombosis and to study in vivo parameters related to hemodynamics and rheology that lead to thrombogenesis. Although no model completely mimics the human condition, much can be learned from existing models about specific biologic processes in disease causation and therapeutic intervention. In general, large animals such as pigs and monkeys have been better suited to study atherosclerosis and arterial and venous thrombosis than smaller species such as rats, rabbits, and dogs. On the other hand, mouse models of arterial and venous thrombosis have attracted increasing interest over the past two decades, owing to direct availability of a growing number of genetically modified mice, improved technical feasibility, standardization of new models of local thrombosis, and low maintenance costs. To simulate rupture of an atherosclerotic plaque, models of arterial thrombosis often involve vascular injury, which can be achieved by several means. There is no animal model that is sufficiently tall, that can mimic the ability of humans to walk upright, and that possesses the calf muscle pump that plays an important role in human venous hemodynamics. A number of spontaneous or genetically engineered animals with overexpression or deletion of various elements in the coagulation, platelet, and fibrinolysis pathways are now available. These animal models can replicate important aspects of thrombosis in humans, and provide a valuable resource in the development of novel concepts of disease mechanisms in human patients.

Arterial thrombosis in mice with factor V Leiden mutation

The factor V Leiden (FVL) mutation has been demonstrated to be associated with the development of venous thrombosis in humans. Whether such a propensity also exists in the arterial circulation remains controversial. In an effort to minimize the variability that clouds the clinical study of arterial thrombosis, we studied FVL-associated arterial thrombosis in an experimental model of homozygous, heterozygous, and wild-type mice. Heterozygous FVL mice were crossbred to C57BL/6J mice over several generations. The genotypes of the resulting three genotype groups (wild type, heterozygous FVL, and homozygous FVL) were blinded to the investigators. Arterial injury was produced with the injection of ferric chloride into an isolated segment of carotid artery. Arterial thrombosis was assessed with an ultrasonic flow probe and the time to occlusion (TTO) was recorded. The carotid artery occluded within 60 minutes of injury in 72 of the animals studied (97.3%). The carotid artery remained patent at 60 minutes in the remaining two animals, both of whom were subsequently found to be genotypically wild type. There was a statistically significant relationship between TTO and genotype (p = .002). TTO was greatest in the wild-type mice (p < .001 vs heterozygous, < .001 vs homozygous) and least in the homozygotes (p < .001 vs heterozygotes). Increased thrombogenicity is present in mice with the FVL mutation and is more prolonged in homozygotes than heterozygotes. These findings provide some corroboration to the clinical studies that suggest an increased risk of arterial events in patients with the FVL mutation.

Hyperglycemia accelerates arterial thrombus formation and attenuates the antithrombotic response to endotoxin in mice

Recent human studies reveal that hyperglycemia induces procoagulant and antifibrinolytic effects in blood that may contribute to a greater risk of arterial thrombosis, but the direct relationship between high blood glucose levels and thrombosis has not yet been investigated. We performed a number of experiments to clarify whether hyperglycemia was causally related to arterial thrombosis and whether the combined stimulus of hyperglycemia and inflammation would enhance the thrombotic effect. In a model of ferric-chloride-induced carotid artery thrombosis, hyperglycemia did not influence the time to occlusion in mice pretreated with streptozotocin, but the rate of thrombus formation was accelerated. This effect was associated with increased thrombin generation and could not be explained by changes in vessel-wall tissue factor activity. The prothrombotic effect of hyperglycemia was assessed in a separate experiment, showing that collagen/thrombin-induced platelet procoagulant activity was increased in hyperglycemic mice. The effect of inflammation was studied by injecting a low dose of endotoxin that caused a systemic inflammatory state after 24 h (increased plasma levels of tumor necrosis factor alpha, interleukin-6 and monocyte chemotactic protein 1 in diabetic and nondiabetic mice) associated with a mild delay in thrombus formation. This reduced rate of thrombus formation was attenuated by hyperglycemia. Together, these data establish a discrete but clear contribution of hyperglycemia in experimental arterial thrombosis.

Development of a calibrated automated thrombography based thrombin generation test in mouse plasma

BACKGROUND

Mouse models have become increasingly important in thrombosis research. However, only a limited number of assays are available for assessment of the coagulation system in mouse plasma.

OBJECTIVES

To quantify tissue factor-initiated thrombin generation in murine platelet-rich and platelet-free plasma and to develop a test for measurement of resistance to activated protein C (APC) in mouse plasma.

METHODS

Thrombin generation was monitored with calibrated automated thrombography (CAT) using a low-affinity fluorogenic substrate for thrombin.

RESULTS

To overcome the higher activity of coagulation inhibitors in mouse plasma as compared with human plasma, the reaction temperature was lowered to 33 degrees C and the assay was carried out at a 2-fold higher final plasma dilution (1:3) than commonly used for CAT in human plasma. This increased the endogenous thrombin potential (ETP) 4- to 5-fold and enabled reliable measurement of thrombin generation in both platelet-free and platelet-rich mouse plasma. For the APC resistance measurement, the reaction conditions were further optimized with respect to tissue factor, phospholipid, APC and CaCl(2) concentrations. The test was validated using plasma of mice with different genetic background with respect to the factor V Leiden mutation (FV Leiden). Mice homozygous for FV Leiden had higher APC sensitivity ratios (mean 5.46; 95% CI 4.88-6.03) than heterozygous FV Leiden mice (mean 4.21; 95% CI 3.53-4.89) and than wild-type mice (mean 2.71; 95%CI 2.15-3.27).

CONCLUSIONS

We have established reaction conditions for measurement of thrombin generation and APC resistance in mouse plasma. This assay enables evaluation of the coagulation system and the function of the protein C system in mouse models.

Melagatran Reduces Advanced Atherosclerotic Lesion Size and May Promote Plaque Stability in Apolipoprotein E– Deficient Mice

OBJECTIVE

Inflammatory mechanisms are involved in atherosclerotic plaque rupture and subsequent thrombin formation. Thrombin not only plays a central role in thrombus formation and platelet activation, but also in the induction of inflammatory processes. We assessed the hypothesis that melagatran, a direct thrombin inhibitor, attenuates plaque progression and promotes stability of advanced atherosclerotic lesions.

METHODS AND RESULTS

Melagatran (500 micromol/kg/d) or control diet was administered to apolipoprotein E-deficient mice (n=54) with advanced atherosclerotic lesions. Treatment reduced lesion progression in brachiocephalic arteries (P<0.005). Morphometric analysis confirmed that thrombin inhibition promoted plaque stability and resulted in thicker fibrous caps (28.4+/-14.2 microm versus 20.8+/-12.0 microm; P<0.05), increased media thickness (29.3+/-9.6 microm versus 24.4+/-6.7 microm; P<0.05), and smaller necrotic cores (73,537+/-41,301 microm2 versus 126,819+/-51,730 microm2; P<0.0005). Electro mobility shift assays revealed reduced binding activity of nuclear factor kappaB (P<0.05) and activator protein-1 (P<0.05) in aortas of treated mice. Furthermore, immunohistochemistry demonstrated reduced staining for matrix metalloproteinase (MMP)-9 (P<0.05). Melagatran had no significant effect on early lesion formation in C57BL/6J mice.

CONCLUSIONS

The direct thrombin inhibitor melagatran reduces lesion size and may promote plaque stability in apolipoprotein E-deficient mice, possibly through reduced activation of proinflammatory transcription factors and reduced synthesis of MMP-9.

Distinct antithrombotic consequences of platelet glycoprotein Ibalpha and VI deficiency in a mouse model of arterial thrombosis

BACKGROUND

Collagen and von Willebrand factor (VWF) are considered essential to initiate platelet deposition at sites of vascular injury, but their respective roles remain to be elucidated.

METHODS

We used a model of carotid artery thrombosis induced by a ferric chloride injury to compare the time to first occlusion and occlusion rate at 25 min postinjury in mice lacking the collagen receptor, glycoprotein (GP) VI, or the ligand-binding domain of the VWF receptor, GP Ibalpha.

RESULTS

In normal mice used as controls (n = 12), a complete obstruction of blood flow developed within 8.05 +/- 0.47 min (mean +/- SEM), and the occlusion rate was 100%. The results were variable in 26 GP VI(-/-) mice. The artery never occluded in eight mice, but the time to first occlusion in the remaining 18 (8.36 +/- 0.27 min) was not different from normal (P = 0.556). Nonetheless, the occlusion rate was 42%, because in seven mice the occluded artery reopened and stayed patent at 25 min. In contrast, the artery never occluded in 12 mice lacking GP Ibalpha. In ex vivo perfusion experiments, GP VI(-/-) platelets failed to form thrombi onto collagen type I fibrils, but formed thrombi of normal size when exposed to endothelial or fibroblast extracellular matrix.

CONCLUSIONS

Absence of GP Ibalpha function has a more profound antithrombotic effect in vivo than absence of the GP VI-dependent pathway of collagen-induced adhesion/activation. Components of the extracellular matrix may elicit a thrombogenic response in the absence of GP VI but not GP Ibalpha.

Analysis of blood coagulation in mice: pre-analytical conditions and evaluation of a home-made assay for thrombin-antithrombin complexes

Background

The use of mouse models for the study of thrombotic disorders has gained increasing importance. Methods for measurement of coagulation activation in mice are, however, scarce. The primary aim of this study was to develop a specific mouse thrombin-antithrombin (TAT) ELISA for measurement of coagulation activation and to compare it with two commercially available assays for human TAT complexes. In addition, we aimed to improve methods for mouse plasma anticoagulation and preparation.

Methods and results

First, for the measurement of TAT-complexes in plasma a mouse specific TAT-ELISA was developed using rabbit polyclonal antibodies raised against mouse thrombin and rat antithrombin, respectively. This ELISA detected an increase in TAT levels in a mouse model of endotoxemia. Two commercial human TAT ELISAs appeared to be less specific for mouse thrombin-rat antithrombin complexes.

Second, to prevent clotting of mouse blood sodium citrate was either mixed with blood during collection in a syringe or was injected intravenously immediately prior to blood collection. Intravenous sodium citrate completely inhibited blood coagulation resulting in plasma with consistently low TAT levels. Sodium citrate mixed with blood during collection resulted in increased TAT levels in 4 out of 16 plasma samples. Third, heparinase was added to plasma samples after in vivo injection of different heparin doses to test its neutralizing effect. Heparinase neutralized up to a 20 U of heparin/mouse and resulted in accurate APTT and factor VIII determinations.

Conclusion

These procedures and reagents for plasma preparation and coagulation testing will improve studies on thrombotic disorders in mice.

Effect of mechanical ventilation on carotid artery thrombosis induced by photochemical injury in mice

BACKGROUND

Increasing use of transgenic and gene targeting techniques for the investigation of hemostasis and vascular biology has generated interest in experimental models of carotid artery thrombosis in mice.

OBJECTIVES

We tested the hypothesis that hypoventilation in anesthetized mice may cause hypercapnia, increased carotid artery blood flow, and altered thrombotic responses to photochemical injury of the carotid artery.

METHODS

Arterial blood gases and carotid artery blood flow were measured in pentobarbital-anesthetized BALB/c or C57BL/6 J mice with and without mechanical ventilation. Photochemical injury of the carotid artery was induced using the rose bengal method.

RESULTS

Compared with ventilated mice, unventilated mice had a 45% increase in carotid artery blood flow (0.74 +/- 0.04 vs. 0.41 +/- 0.03 mL min-1; P < 0.001) that was associated with an elevation of arterial PCO2 (58 +/- 4 vs. 33 +/- 4 mmHg; P < 0.05) and a decrease in arterial pH (7.18 +/- 0.05 vs. 7.32 +/- 0.03; P < 0.05). Time to first occlusion of the carotid artery after photochemical injury was shorter in ventilated than in unventilated mice (29 +/- 6 vs. 73 +/- 9 min; P < 0.001). Time to stable occlusion was also shorter in ventilated mice (49 +/- 8 vs. 81 +/- 6 min; P < 0.05). Elevated carotid artery blood flow, hypercarbic acidosis, and prolonged occlusion times also were observed in mice ventilated with supplemental carbon dioxide.

CONCLUSIONS

General anesthesia without mechanical ventilation has the potential to confound studies of experimental thrombosis in vivo by producing hypoventilation, hypercapnia, acidosis, and altered carotid artery blood flow. Mechanical ventilation with maintenance of normal blood gases may enhance the physiological insight gained from experimental models of carotid artery thrombosis in mice.

Aortic constriction exacerbates atherosclerosis and induces cardiac dysfunction in mice lacking apolipoprotein E

Despite considerable evidence suggesting that hypertension contributes to the development and progression of atherosclerosis, the causative links remain unclear. We have tested the effects of chronic hypertension induced by suprarenal aortic constriction on the development of atherosclerosis in apolipoprotein E-deficient (Apoe-/-) mice. Compared with a sham operation, narrowing the aortic luminal diameter by 33% increased blood pressure proximal to the constriction by approximately 15 mm Hg, but the pressures distal to the constriction were unchanged. Kidney renin mRNA and plasma renin activity were also unaffected. Compared with plaque size after the sham operation, atherosclerotic plaque size in the aortic root 8 weeks after coarctation was increased to 245% and 152% in males and females, respectively. Aortic segments at the constriction were free of atherosclerotic deposits, but segments proximal to the constriction were dilated and had atherosclerotic lesions. Thrombi were present immediately below the constriction in Apoe-/- and wild-type vessels. Surprisingly, compared with wild-type mice, the Apoe-/- mice were more susceptible to the cardiac hypertrophy and dysfunction induced by pressure overload. Thus, aortic coarctation exacerbates atherosclerosis in vessels proximal to the constriction without a concomitant increase in the renin-angiotensin system. Our study also suggests that apolipoprotein E plays an important role in modulating cardiac hypertrophy.