Removal of endothelial surface-associated von villebrand factor suppresses accelerate datherosclerosis after myocardial infarction.

BACKGROUND: Thromboinflammation involving platelet adhesion to endothelial surface-associated von Willebrand factor (VWF) has been implicated in the accelerated progression of non-culprit plaques after MI. The aim of this study was to use arterial endothelial molecular imaging to mechanistically evaluate endothelial-associated VWF as a therapeutic target for reducing remote plaque activation after myocardial infarction (MI). METHODS: Hyperlipidemic mice deficient for the low-density lipoprotein receptor and Apobec-1 underwent closed-chest MI and were treated chronically with either: (i) recombinant ADAMTS13 which is responsible for proteolytic removal of VWF from the endothelial surface, (ii) N-acetylcysteine (NAC) which removes VWF by disulfide bond reduction, (iii) function-blocking anti-factor XI (FXI) antibody, or (iv) no therapy. Non-ischemic controls were also studied. At day 3 and 21, ultrasound molecular imaging was performed with probes targeted to endothelial-associated VWF A1-domain, platelet GPIbα, P-selectin and vascular cell adhesion molecule-1 (VCAM-1) at lesion-prone sites of the aorta. Histology was performed at day 21. RESULTS: Aortic signal for P-selectin, VCAM-1, VWF, and platelet-GPIbα were all increased several-fold (p < 0.01) in post-MI mice versus sham-treated animals at day 3 and 21. Treatment with NAC and ADAMTS13 significantly attenuated the post-MI increase for all four molecular targets by > 50% (p < 0.05 vs. non-treated at day 3 and 21). On aortic root histology, mice undergoing MI versus controls had 2-4 fold greater plaque size and macrophage content (p < 0.05), approximately 20-fold greater platelet adhesion (p < 0.05), and increased staining for markers of platelet transforming growth factor-ß1 signaling. Accelerated plaque growth and inflammatory activation was almost entirely prevented by ADAMTS13 and NAC. Inhibition of FXI had no significant effect on molecular imaging signal or plaque morphology. CONCLUSIONS: Plaque inflammatory activation in remote arteries after MI is strongly influenced by VWF-mediated platelet adhesion to the endothelium. These findings support investigation into new secondary preventive therapies for reducing non-culprit artery events after MI.

Elevated LDL Cholesterol Increases Microvascular Endothelial VWF and Thromboinflammation After Myocardial Infarction.

BACKGROUND: In reperfused myocardial infarction, VWF (von Willebrand factor)-mediated platelet adhesion contributes to impaired microvascular reflow and possibly also to postmyocardial infarction inflammation. We hypothesized that postischemic thromboinflammatory processes are worsened by elevated LDL (low-density lipoprotein) cholesterol. METHODS: Myocardial ischemia-reperfusion or sham procedure was performed in wild-type mice and hyperlipidemic mice deficient for the LDL receptor and Apobec-1 (apolipoprotein-B mRNA editing enzyme catalytic polypeptide-1; DKO [double knockout]). DKO subgroups were treated with N-acetylcysteine, which inhibits pro-adhesive VWF multimers or with recombinant ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin motifs-13), which enzymatically cleaves endothelial surface-associated VWF. Myocardial contrast echocardiography perfusion imaging and molecular imaging for VWF, platelet glycoprotein Ibα, and leukocyte CD18 (cluster of differentiation) were performed 30 minutes post-reperfusion. Histology, infarct sizing, and echocardiography were performed at 1.5 or 72 hours; late echocardiography was performed at day 21. RESULTS: After ischemia-reperfusion, DKO compared with wild-type mice had ≈2-fold higher (P<0.05) risk area signal for microvascular platelet adhesion, VWF, and CD18; greater impairment in microvascular reflow, and 2-fold larger infarct size. Treatment of DKO mice with N-acetylcysteine and ADAMTS13 reduced molecular imaging signal for microvascular platelet adhesion, VWF, and CD18; improved early microvascular reflow; and reduced eventual infarct size. ADAMTS13 suppressed the postmyocardial infarction neutrophil and monocyte infiltration, enhanced the time-dependent recovery of left ventricular systolic function, and prevented late left ventricular remodeling. CONCLUSIONS: In reperfused myocardial infarction, elevated LDL cholesterol promotes thromboinflammation through excess microvascular endothelial VWF and platelet adhesion, resulting in less microvascular reflow and larger infarct size. In the presence of elevated LDL cholesterol, therapies that suppress endothelial-associated VWF can promote recovery of left ventricular function and protect against remodeling.

Thrombotic microangiopathy as a cause of cardiovascular toxicity from the BCR-ABL1 tyrosine kinase inhibitor ponatinib.

The third-generation tyrosine kinase inhibitor (TKI) ponatinib has been associated with high rates of acute ischemic events. The pathophysiology responsible for these events is unknown. We hypothesized that ponatinib produces an endothelial angiopathy involving excessive endothelial-associated von Willebrand factor (VWF) and secondary platelet adhesion. In wild-type mice and ApoE-/- mice on a Western diet, ultrasound molecular imaging of the thoracic aorta for VWF A1-domain and glycoprotein-Ibα was performed to quantify endothelial-associated VWF and platelet adhesion. After treatment of wild-type mice for 7 days, aortic molecular signal for endothelial-associated VWF and platelet adhesion were five- to sixfold higher in ponatinib vs sham therapy (P < .001), whereas dasatinib had no effect. In ApoE-/- mice, aortic VWF and platelet signals were two- to fourfold higher for ponatinib-treated compared with sham-treated mice (P < .05) and were significantly higher than in treated wild-type mice (P < .05). Platelet and VWF signals in ponatinib-treated mice were significantly reduced by N-acetylcysteine and completely eliminated by recombinant ADAMTS13. Ponatinib produced segmental left ventricular wall motion abnormalities in 33% of wild-type and 45% of ApoE-/- mice and corresponding patchy perfusion defects, yet coronary arteries were normal on angiography. Instead, a global microvascular angiopathy was detected by immunohistochemistry and by intravital microscopy observation of platelet aggregates and nets associated with endothelial cells and leukocytes. Our findings reveal a new form of vascular toxicity for the TKI ponatinib that involves VWF-mediated platelet adhesion and a secondary microvascular angiopathy that produces ischemic wall motion abnormalities. These processes can be mitigated by interventions known to reduce VWF multimer size.

Augmentation of Muscle Blood Flow by Ultrasound Cavitation Is Mediated by ATP and Purinergic Signaling.

BACKGROUND: Augmentation of tissue blood flow by therapeutic ultrasound is thought to rely on convective shear. Microbubble contrast agents that undergo ultrasound-mediated cavitation markedly amplify these effects. We hypothesized that purinergic signaling is responsible for shear-dependent increases in muscle perfusion during therapeutic cavitation. METHODS: Unilateral exposure of the proximal hindlimb of mice (with or without ischemia produced by iliac ligation) to therapeutic ultrasound (1.3 MHz, mechanical index 1.3) was performed for 10 minutes after intravenous injection of 2×108 lipid microbubbles. Microvascular perfusion was evaluated by low-power contrast ultrasound perfusion imaging. In vivo muscle ATP release and in vitro ATP release from endothelial cells or erythrocytes were assessed by a luciferin-luciferase assay. Purinergic signaling pathways were assessed by studying interventions that (1) accelerated ATP degradation; (2) inhibited P2Y receptors, adenosine receptors, or KATP channels; or (3) inhibited downstream signaling pathways involving endothelial nitric oxide synthase or prostanoid production (indomethacin). Augmentation in muscle perfusion by ultrasound cavitation was assessed in a proof-of-concept clinical trial in 12 subjects with stable sickle cell disease. RESULTS: Therapeutic ultrasound cavitation increased muscle perfusion by 7-fold in normal mice, reversed tissue ischemia for up to 24 hours in the murine model of peripheral artery disease, and doubled muscle perfusion in patients with sickle cell disease. Augmentation in flow extended well beyond the region of ultrasound exposure. Ultrasound cavitation produced an ≈40-fold focal and sustained increase in ATP, the source of which included both endothelial cells and erythrocytes. Inhibitory studies indicated that ATP was a critical mediator of flow augmentation that acts primarily through either P2Y receptors or adenosine produced by ectonucleotidase activity. Combined indomethacin and inhibition of endothelial nitric oxide synthase abolished the effects of therapeutic ultrasound, indicating downstream signaling through both nitric oxide and prostaglandins. CONCLUSIONS: Therapeutic ultrasound using microbubble cavitation to increase muscle perfusion relies on shear-dependent increases in ATP, which can act through a diverse portfolio of purinergic signaling pathways. These events can reverse hindlimb ischemia in mice for >24 hours and increase muscle blood flow in patients with sickle cell disease. CLINICAL TRIAL REGISTRATION: URL: http://clinicaltrials.gov. Unique identifier: NCT01566890.

Molecular imaging of the paracrine proangiogenic effects of progenitor cell therapy in limb ischemia.

BACKGROUND: Stem cells are thought to enhance vascular remodeling in ischemic tissue in part through paracrine effects. Using molecular imaging, we tested the hypothesis that treatment of limb ischemia with multipotential adult progenitor cells (MAPCs) promotes recovery of blood flow through the recruitment of proangiogenic monocytes. METHODS AND RESULTS: Hind-limb ischemia was produced in mice by iliac artery ligation, and MAPCs were administered intramuscularly on day 1. Optical imaging of luciferase-transfected MAPCs indicated that cells survived for 1 week. Contrast-enhanced ultrasound on days 3, 7, and 21 showed a more complete recovery of blood flow and greater expansion of microvascular blood volume in MAPC-treated mice than in controls. Fluorescent microangiography demonstrated more complete distribution of flow to microvascular units in MAPC-treated mice. On ultrasound molecular imaging, expression of endothelial P-selectin and intravascular recruitment of CX(3)CR-1-positive monocytes were significantly higher in MAPC-treated mice than in the control groups at days 3 and 7 after arterial ligation. Muscle immunohistology showed a >10-fold-greater infiltration of monocytes in MAPC-treated than control-treated ischemic limbs at all time points. Intravital microscopy of ischemic or tumor necrosis factor-α-treated cremaster muscle demonstrated that MAPCs migrate to perimicrovascular locations and potentiate selectin-dependent leukocyte rolling. In vitro migration of human CD14(+) monocytes was 10-fold greater in response to MAPC-conditioned than basal media. CONCLUSIONS: In limb ischemia, MAPCs stimulate the recruitment of proangiogenic monocytes through endothelial activation and enhanced chemotaxis. These responses are sustained beyond the MAPC lifespan, suggesting that paracrine effects promote flow recovery by rebalancing the immune response toward a more regenerative phenotype.

Epoxyeicosatrienoic acids mediate insulin-mediated augmentation in skeletal muscle perfusion and blood volume.

Skeletal muscle microvascular blood flow (MBF) increases in response to physiological hyperinsulinemia. This vascular action of insulin may facilitate glucose uptake. We hypothesized that epoxyeicosatrienoic acids (EETs), a family of arachadonic, acid-derived, endothelium-derived hyperpolarizing factors, are mediators of insulin's microvascular effects. Contrast-enhanced ultrasound (CEU) was performed to quantify skeletal muscle capillary blood volume (CBV) and MBF in wild-type and obese insulin-resistant (db/db) mice after administration of vehicle or trans-4-[4-(3-adamantan-1-ylureido)cyclohexyloxy]benzoic acid (t-AUCB), an inhibitor of soluble epoxide hydrolase that converts EETs to less active dihydroxyeicosatrienoic acids. Similar studies were performed in rats pretreated with l-NAME. CEU was also performed in rats undergoing a euglycemic hyperinsulinemic clamp, half of which were pretreated with the epoxygenase inhibitor MS-PPOH to inhibit EET synthesis. In both wild-type and db/db mice, intravenous t-AUCB produced an increase in CBV (65-100% increase at 30 min, P < 0.05) and in MBF. In db/db mice, t-AUCB also reduced plasma glucose by ∼15%. In rats pretreated with l-NAME, t-AUCB after produced a significant ≈20% increase in CBV, indicating a component of vascular response independent of nitric oxide (NO) production. Hyperinsulinemic clamp produced a time-dependent increase in MBF (19 ± 36 and 76 ± 49% at 90 min, P = 0.026) that was mediated in part by an increase in CBV. Insulin-mediated changes in both CBV and MBF during the clamp were blocked entirely by MS-PPOH. We conclude that EETs are a mediator of insulin-mediated augmentation in skeletal muscle perfusion and are involved in regulating changes in CBV during hyperinsulinemia.

Molecular imaging reveals rapid reduction of endothelial activation in early atherosclerosis with apocynin independent of antioxidative properties.

OBJECTIVE: Antioxidative drugs continue to be developed for the treatment of atherosclerosis. Apocynin is an nicotinamide adenine dinucleotide phosphate oxidase inhibitor with anti-inflammatory properties. We used contrast-enhanced ultrasound molecular imaging to assess whether short-term apocynin therapy in atherosclerosis reduces vascular oxidative stress and endothelial activation APPROACH AND RESULTS: Genetically modified mice with early atherosclerosis were studied at baseline and after 7 days of therapy with apocynin (4 mg/kg per day IP) or saline. Contrast-enhanced ultrasound molecular imaging of the aorta was performed with microbubbles targeted to vascular cell adhesion molecule 1 (VCAM-1; MB(V)), to platelet glycoprotein Ibα (MB(Pl)), and control microbubbles (MB(Ctr)). Aortic vascular cell adhesion molecule 1 was measured using Western blot. Aortic reactive oxygen species generation was measured using a lucigenin assay. Hydroethidine oxidation was used to assess aortic superoxide generation. Baseline signal for MBV (1.3 ± 0.3 AU) and MB(Pl )(1.5 ± 0.5 AU) was higher than for MBCtr (0.5 ± 0.2 AU; P<0.01). In saline-treated animals, signal did not significantly change for any microbubble agent, whereas short-term apocynin significantly (P<0.05) reduced vascular cell adhesion molecule 1 and platelet signal (MBV: 0.3 ± 0.1; MBPl: 0.4 ± 0.1; MBCtr: 0.3 ± 0.2 AU; P=0.6 between agents). Apocynin reduced aortic vascular cell adhesion molecule 1 expression by 50% (P<0.05). However, apocynin therapy did not reduce reactive oxygen species content, superoxide generation, or macrophage content. CONCLUSIONS: Short-term treatment with apocynin in atherosclerosis reduces endothelial cell adhesion molecule expression. This change in endothelial phenotype can be detected by molecular imaging before any measurable decrease in macrophage content and is not associated with a detectable change in oxidative burden.

Influence of Atherosclerotic Risk Factors on the Effectiveness of Therapeutic Ultrasound Cavitation for Flow Augmentation.

BACKGROUND: Shear created by inertial cavitation of microbubbles by ultrasound augments limb and myocardial perfusion and can reverse tissue ischemia. Our aim was to determine whether this therapeutic bioeffect is attenuated by atherosclerotic risk factors that are known to impair shear-mediated vasodilation and adversely affect microvascular reactivity. METHODS: In mice, lipid-stabilized decafluorobutane microbubbles (2 × 108) were administered intravenously while exposing a proximal hind limb to ultrasound (1.3 MHz, 1.3 mechanical index, pulsing interval 5 seconds) for 10 minutes. Murine strains included wild-type mice and severely hyperlipidemic mice at 15, 35, or 52 weeks of age as a model of aging and elevated cholesterol, and obese db/db mice (≈15 weeks) with severe insulin resistance. Quantitative contrast-enhanced ultrasound perfusion imaging was performed to assess microvascular perfusion in the control and ultrasound-exposed limb. An in situ electrochemical probe and in vivo biophotonic imaging were used to assess limb nitric oxide (NO) and adenosine triphosphosphate concentrations, respectively. RESULTS: Microvascular perfusion was significantly increased by several fold in the cavitation-exposed limb versus control limb for all murine strains and ages (P < .001). In wild-type and hyperlipidemic mice, hyperemia from cavitation was attenuated in the 2 older age groups (P < .01). In young mice (15 weeks), perfusion in cavitation-exposed muscle was less in both the hyperlipidemic mice and the obese db/db mice compared with corresponding wild-type mice. Using young hyperlipidemic mice as a model for flow impairment, limb NO production after cavitation was reduced but adenosine triphosphosphate production was unaltered when compared with age-matched wild-type mice. CONCLUSIONS: In mice, ultrasound cavitation of microbubbles increases limb perfusion by several fold even in the presence of traditional atherosclerotic risk factors. However, older age, hyperlipidemia, and insulin resistance modestly attenuate the degree of flow augmentation, which could impact the degree of flow response in current clinical trials in patients with critical limb ischemia.

Dysregulated selectin expression and monocyte recruitment during ischemia-related vascular remodeling in diabetes mellitus.

OBJECTIVE: Diabetes mellitus (DM) is associated with impaired ischemia-related vascular remodeling and also dysregulation of the inflammatory response. We sought to determine whether impaired selectin-mediated monocyte recruitment in ischemic tissues contributes to blunted ischemia-mediated angiogenesis in DM. METHODS AND RESULTS: Contrast-enhanced ultrasound perfusion imaging and molecular imaging of endothelial P-selectin expression in the proximal hindlimb were performed at 1, 3, and 21 days after arterial ligation in wild-type and db/db mice. Ligation reduced muscle blood flow to ≈0.05 mL/minute per gram in both strains. Significant recovery of flow occurred only in wild-type mice (60%-65% of baseline flow). On molecular imaging, baseline P-selectin signal was 4-fold higher in db/db compared with wild-type mice (P<0.01) but increased minimally at day 1 after ischemia, whereas signal increased approximately 10-fold in wild-type mice (P<0.01). Immunohistology of the hindlimb skeletal muscle demonstrated severely reduced monocyte recruitment in db/db mice compared with wild-type mice. Local treatment with monocyte chemotactic protein-1 corrected the deficits in postischemic P-selectin expression and monocyte recruitment in db/db mice and led to greater recovery in blood flow. CONCLUSION: In DM, there is dysregulation of the selectin response to limb ischemia, which leads to impaired monocyte recruitment, which may be mechanistically related to reduced vascular remodeling in limb ischemia.

Reduced Proteolytic Cleavage of von Willebrand Factor Leads to Aortic Valve Stenosis and Load-Dependent Ventricular Remodeling.

We hypothesized that excess endothelial-associated von Willebrand factor (vWF) and secondary platelet adhesion contribute to aortic valve stenosis (AS). We studied hyperlipidemic mice lacking ADAMTS13 (LDLR -/- AD13 -/- ), which cleaves endothelial-associated vWF multimers. On echocardiography and molecular imaging, LDLR -/- AD13 -/- compared with control strains had increased aortic endothelial vWF and platelet adhesion and developed hemodynamically significant AS, arterial stiffening, high valvulo-aortic impedance, and secondary load-dependent reduction in LV systolic function. Histology revealed leaflet thickening and calcification with valve interstitial cell myofibroblastic and osteogenic transformation, and evidence for TGFß1 pathway activation. We conclude that valve leaflet endothelial vWF-platelet interactions promote AS through juxtacrine platelet signaling.

Ibrutinib Inhibits BMX-Dependent Endothelial VCAM-1 Expression In Vitro and Pro-Atherosclerotic Endothelial Activation and Platelet Adhesion In Vivo.

Introduction: Inflammatory activation of the vascular endothelium leads to overexpression of adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), contributing to the pro-thrombotic state underpinning atherogenesis. While the role of TEC family kinases (TFKs) in mediating inflammatory cell and platelet activation is well defined, the role of TFKs in vascular endothelial activation remains unclear. We investigated the role of TFKs in endothelial cell activation in vitro and in a nonhuman primate model of diet-induced atherosclerosis in vivo. Methods and Results: In vitro, we found that ibrutinib blocked activation of the TFK member, BMX, by vascular endothelial growth factors (VEGF)-A in human aortic endothelial cells (HAECs). Blockade of BMX activation with ibrutinib or pharmacologically distinct BMX inhibitors eliminated the ability of VEGF-A to stimulate VCAM-1 expression in HAECs. We validated that treatment with ibrutinib inhibited TFK-mediated platelet activation and aggregation in both human and primate samples as measured using flow cytometry and light transmission aggregometry. We utilized contrast-enhanced ultrasound molecular imaging to measure platelet GPIbα and endothelial VCAM-1 expression in atherosclerosis-prone carotid arteries of obese nonhuman primates. We observed that the TFK inhibitor, ibrutinib, inhibited platelet deposition and endothelial cell activation in vivo. Conclusion: Herein we found that VEGF-A signals through BMX to induce VCAM-1 expression in endothelial cells, and that VCAM-1 expression is sensitive to ibrutinib in vitro and in atherosclerosis-prone carotid arteries in vivo. These findings suggest that TFKs may contribute to the pathogenesis of atherosclerosis and could represent a novel therapeutic target.

Molecular imaging of the initial inflammatory response in atherosclerosis: implications for early detection of disease.

UNLABELLED: Background- We hypothesized that molecular imaging of endothelial cell adhesion molecule expression could noninvasively evaluate prelesion atherogenic phenotype. METHODS AND RESULTS: Mice deficient for the LDL-receptor and the Apobec-1 editing peptide (DKO mice) were studied as an age-dependent model of atherosclerosis. At 10, 20, and 40 weeks of age, ultrasound molecular imaging of the proximal thoracic aorta was performed with contrast agents targeted to P-selectin and VCAM-1. Atherosclerotic lesion severity and content were assessed by ultrahigh frequency ultrasound, histology, and immunohistochemistry. In wild-type mice at all ages, there was neither aortic thickening nor targeted tracer signal enhancement. In DKO mice, lesions progressed from sparse mild intimal thickening at 10 weeks to widespread severe lesions with luminal encroachment at 40 weeks. Molecular imaging for P-selectin and VCAM-1 demonstrated selective signal enhancement (P<0.01 versus nontargeted agent) at all ages for DKO mice. P-selectin and VCAM-1 signal in DKO mice were greater by 3-fold at 10 weeks, 4- to 6-fold at 20 weeks, and 9- to 10-fold at 40 weeks compared to wild-type mice. En face microscopy demonstrated preferential attachment of targeted microbubbles to regions of lesion formation. CONCLUSIONS: Noninvasive ultrasound molecular imaging of endothelial activation can detect lesion-prone vascular phenotype before the appearance of obstructive atherosclerotic lesions.

Treatment of Limb Ischemia with Conducted Effects of Catheter-Based Endovascular Ultrasound.

Ultrasound (US) is known to stimulate endogenous shear-dependent pathways, and can lower microvascular resistance through mediators that are conducted downstream from US exposure. We hypothesized that endovascular US, already in use for thrombolysis in humans, can improve tissue perfusion in the setting of acute limb ischemia through downstream-conducted effects. Models of severe peripheral arterial disease were developed in mice and in rhesus macaques. An endovascular US catheter (2.3 MHz, 0.5-1.1 MPa) was used to expose the limb adductor in mice for 10 min or the femoral artery distal to stenosis in macaques for 15 min. Quantitative contrast-enhanced ultrasound perfusion imaging was performed to assess flow augmentation in the adductor muscle of mice and the calf muscle of macaques. Microvascular blood flow in the ischemic limb relative to the contralateral control limb was reduced to 22 ± 8% in mice and 36 ± 20% in macaques. US produced immediate 2.3- and 3-fold increases (p < 0.05) in the murine and macaque ischemic limbs, respectively. In macaques, perfusion in the ischemic limb was increased to a normal level. We conclude that non-cavitating US produced by endovascular catheters that are used to enhance thrombolysis in humans can reduce vascular resistance and increase limb perfusion in the setting of acute ischemia.

Echocardiographic Molecular Imaging of the Effect of Anticytokine Therapy for Atherosclerosis.

BACKGROUND: Echocardiographic molecular imaging techniques are beginning to be applied to evaluate preclinical efficacy of new drugs. In a large clinical trial, anti-interleukin-1ß (IL-1ß) immunotherapy reduced atherosclerotic events, yet treatment effects were modest, and the mechanisms of action were not fully elucidated. We tested the hypothesis that echocardiographic molecular imaging can assess changes in vascular thromboinflammatory status in response to anti-IL-1ß therapy. METHODS: In wild-type and atherosclerotic mice deficient for the low-density lipoprotein-receptor and Apobec-1, closed-chest myocardial infarction (MI) was performed to mimic high-risk clinical cohorts. Control animals had sham surgery. Post-MI animals were randomized to either no therapy or anti-IL-1ß immunotherapy, which was continued weekly. At post-MI day 3 or 21, in vivo ultrasound molecular imaging of aortic VCAM-1, P-selectin, von Willebrand factor A1-domain, and platelet GPIbα in the thoracic aorta was performed. Aortic histology and NF-κB activity were assessed in atherosclerotic mice. RESULTS: In both atherosclerotic and wild-type mice, MI produced a several-fold increase (P < .05) in aortic molecular signals for P-selectin, VCAM-1, von Willebrand factor, and GPIbα. In atherosclerotic mice, signal remained elevated at day 21. Anti-IL-1ß therapy completely abolished the post-MI increase in signal for all endothelial targets (P < .05 vs nontreated) at day 3 and 21. In atherosclerotic mice, MI triggered an increase in aortic plaque growth and macrophage content, a decrease in plaque collagen, and elevated aortic NF-κB (P < .05 for all changes). All of these remote plaque adverse changes were inhibited by anti-IL-1ß therapy. CONCLUSIONS: Echocardiographic molecular imaging of the vascular endothelium can quantify the beneficial effects of therapies designed to suppress the proatherosclerotic arterial thromboinflammatory effects of alarmins such as IL-1ß. This approach could potentially be used to evaluate the biologic variables that influence response in preclinical studies, and possibly to select patients most likely to benefit from therapy.

Regional and Conducted Vascular Effects of Endovascular Ultrasound Catheters.

Intra-vascular ultrasound catheters are used clinically to facilitate clot lysis. We hypothesized that these devices could also directly lower microvascular resistance and increase tissue perfusion through established shear-dependent pathways. In mice, either the proximal hind-limb muscles or the upstream femoral artery alone was exposed to an endovascular ultrasound catheter (2.3 MHz, 0.5-1.1 MPa) for 10 min. Quantitative microvascular perfusion imaging in the hind limbs exposed to the endovascular ultrasound system exhibited a more-than-twofold increase in flow (p < 0.01) compared with the contralateral control limb after exposure of either the muscle or the femoral artery alone. Using an in vivo optical imaging reporting system, an eight- to ninefold increase in tissue adenosine triphosphate (ATP) was detected in the region of insonification (p = 0.006). Ultrasound was found to produce an immediate release of ATP from ex vivo erythrocytes (p = 0.03). In situ electrochemical sensing revealed an immediate increase in nitric oxide with initiation of ultrasound which returned to baseline within 5 min of termination, as well as ultrasound-triggered nitric oxide (NO) release from erythrocytes. These data indicate that non-cavitating ultrasound produced by endovascular catheters can reduce vascular resistance and increase flow through recognized shear-dependent vasodilator pathways involving purinergic signaling and NO.

Proteolysis of Von Willebrand Factor Influences Inflammatory Endothelial Activation and Vascular Compliance in Atherosclerosis.

This study used in vivo molecular imaging to characterize endotheliall activation attributable to von Willebrand factor (vWF)-mediated platelet adhesion in atherosclerosis. In atherosclerotic mice lacking the low-density lipoprotein receptor on Western diet, the additional genetic deletion of the ADAMTS13, which cleaves endothelial-associated vWF, produced greater aortic molecular imaging signal for not only vWF and platelets, but also for endothelial adhesion molecules VCAM1 and P-selectin, larger plaque size, and lower aortic distensibility. Sustained ADAMTS13 therapy reduced signal for all 4 molecular targets and plaque size. We conclude that excess endothelial-associated vWF contributes to not only platelet adhesion, but also to up-regulation of endothelial cell adhesion molecules.

Flow Augmentation in the Myocardium by Ultrasound Cavitation of Microbubbles: Role of Shear-Mediated Purinergic Signaling.

BACKGROUND: Ultrasound-mediated cavitation of microbubble contrast agents produces high intravascular shear. We hypothesized that microbubble cavitation increases myocardial microvascular perfusion through shear-dependent purinergic pathways downstream from ATP release that is immediate and sustained through cellular ATP channels such as Pannexin-1. METHODS: Quantitative myocardial contrast echocardiography perfusion imaging and in vivo optical imaging of ATP was performed in wild-type and Pannexin-1-deficient (Panx1-/-) mice before and 5 and 30 minutes after 10 minutes of ultrasound-mediated (1.3 MHz, mechanical index 1.3) myocardial microbubble cavitation. Flow augmentation in a preclinical model closer to humans was evaluated in rhesus macaques undergoing myocardial contrast echocardiography perfusion imaging after high-power cavitation in the apical four-chamber plane for 10 minutes. RESULTS: Microbubble cavitation in wild-type mice (n = 7) increased myocardial perfusion by 64% ± 25% at 5 minutes and 95% ± 55% at 30 minutes compared with baseline (P < .05). In Panx1-/- mice (n = 5), perfusion increased by 28% ± 26% at 5 minutes (P = .04) but returned to baseline at 30 minutes. Myocardial ATP signal in wild-type (n = 7) mice undergoing cavitation compared with sham-treated controls (n = 3) was 450-fold higher at 5 minutes and 90-fold higher at 30 minutes after cavitation (P < .001). The ATP signal in Panx1-/- mice (n = 4) was consistently 10-fold lower than that in wild-type mice and was similar to sham controls at 30 minutes. In macaques (n = 8), myocardial perfusion increased twofold in the cavitation-exposed four-chamber plane, similar in degree to that produced by adenosine, but did not increase in the control two-chamber plane. CONCLUSIONS: Cavitation of microbubbles in the myocardial microcirculation produces an immediate release of ATP, likely from cell microporation, as well as sustained release, which is channel dependent and responsible for persistent flow augmentation. These findings provide mechanistic insight by which cavitation improves perfusion and reduces infarct size in patients with myocardial infarction.

Molecular imaging of inflammation in atherosclerosis with targeted ultrasound detection of vascular cell adhesion molecule-1.

BACKGROUND: The ability to image vascular inflammatory responses may allow early diagnosis and treatment of atherosclerosis. We hypothesized that molecular imaging of vascular cell adhesion molecule-1 (VCAM-1) expression with contrast-enhanced ultrasound (CEU) could be used for this purpose. METHODS AND RESULTS: Attachment of VCAM-1-targeted and control microbubbles to cultured endothelial cells was assessed in a flow chamber at variable shear stress (0.5 to 12.0 dynes/cm2). Microbubble attachment to aortic plaque was determined by en face microscopy of the thoracic aorta 10 minutes after intravenous injection in wild-type or apolipoprotein E-deficient mice on either chow or hypercholesterolemic diet. CEU molecular imaging of the thoracic aorta 10 minutes after intravenous microbubble injection was performed for the same animal groups. VCAM-1-targeted but not control microbubbles attached to cultured endothelial cells, although firm attachment at the highest shear rates (8 to 12 dynes/cm2) occurred only in pulsatile flow conditions. Aortic attachment of microbubbles and targeted CEU signal was very low in control wild-type mice on chow diet. Aortic attachment of microbubbles and CEU signal for VCAM-1-targeted microbubbles differed between treatment groups according to extent of VCAM-1-positive plaque formation (median CEU videointensity, 1.8 [95% CI, 1.2 to 1.7], 3.7 [95% CI, 2.9 to 7.3], 6.8 [95% CI, 3.9 to 7.6], and 11.2 [95% CI, 8.5 to 16.0] for wild-type mice on chow and hypercholesterolemic diet and for apolipoprotein E-deficient mice on chow and hypercholesterolemic diet, respectively; P<0.001). CONCLUSIONS: CEU molecular imaging of VCAM-1 is capable of rapidly quantifying vascular inflammatory changes that occur in different stages of atherosclerosis. This method may be potentially useful for early risk stratification according to inflammatory phenotype.

Assessment of Novel Antioxidant Therapy in Atherosclerosis by Contrast Ultrasound Molecular Imaging.

BACKGROUND: Ultrasound molecular imaging was used to evaluate the therapeutic effects of antioxidant therapy with EUK-207, which has superoxide dismutase and catalase activities, on suppressing high-risk atherosclerotic features. METHODS: Mice with age-dependent atherosclerosis produced by deletion of the low-density lipoprotein receptor and Apobec-1 were studied at 20 and 40 weeks of age. EUK-207 or vehicle was administered for the preceding 8 weeks. Therapy for 28 weeks was also studied for 40-week-old mice. Ultrasound molecular imaging of the thoracic aorta was performed with contrast agents targeted to endothelial P-selectin, von Willebrand factor A1-domain, and platelet glycoprotein Ibα or control agent. Aortic plaque area and macrophage content were assessed by histology. RESULTS: In 20-week-old double-knockout mice, EUK-207 compared with sham therapy produced only nonsignificant trends for reduction in molecular imaging signal for endothelial P-selectin, von Willebrand factor A1-domain, and platelet adhesion. At 40 weeks, EUK-207 given for 8 or 28 weeks significantly (P < .05) reduced signal for all three endothelial-associated events essentially to background levels, with the exception of glycoprotein Ibα signal after 8 weeks (P = .06). On aortic histology, EUK-207 therapy for 8 weeks did not affect plaque area or macrophage content at either age. However, EUK-207 for 28 weeks almost completely suppressed plaque development (350 ± 258 vs 4 ± 6 × 103 µm2, P = .014) and macrophage content (136 ± 103 vs 3 ± 2 × 103 µm2, P = .002) compared with control mice at 40 weeks. CONCLUSIONS: Molecular imaging can be used to assess vascular responses to antioxidants and has demonstrated that certain antioxidants reduce vascular endothelial activation and platelet adhesion, but reductions in plaque size and macrophage content occurs only with long-duration therapy that is started early.

Molecular Imaging of VWF (von Willebrand Factor) and Platelet Adhesion in Postischemic Impaired Microvascular Reflow.

BACKGROUND: Complete mechanistic understanding of impaired microvascular reflow after myocardial infarction will likely lead to new therapies for reducing infarct size. Myocardial contrast echocardiography perfusion imaging and molecular imaging were used to evaluate the contribution of microvascular endothelial-associated VWF (von Willebrand factor) and platelet adhesion to microvascular no-reflow. METHODS AND RESULTS: Myocardial infarction was produced by transient LAD ligation in WT (wild type) mice, WT mice treated with the VWF proteolytic enzyme ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13), and ADAMTS13-deficient (ADAMTS13-/-) mice. Myocardial contrast echocardiography perfusion imaging and molecular imaging of VWF and platelet GP (glycoprotein) Ibα were performed 30 minutes after ischemia-reperfusion. Infarct size was measured at 3 days. Mortality during ischemia-reperfusion incrementally increased in WT+ADAMTS13, WT, and ADAMTS13-/- mice (14%, 43%, and 63%, respectively; P<0.05). For WT mice, molecular imaging signal for platelets and VWF in the postischemic risk area was 4- to 5-fold higher ( P<0.05) compared with both the remote nonischemic regions or to sham-treated mice. Signal enhancement in the risk area was completely abolished by ADAMTS13 treatment for both platelets (12.8±3.3 versus -1.0±4.4 IU; P<0.05) and VWF (13.9±4.0 versus -1.0±3.0 IU; P<0.05). ADAMTS13-/- compared with WT mice had 2- to 3-fold higher risk area signal for platelets (33.1±8.5 IU) and VWF (30.9±1.9 IU). Microvascular reflow in the risk area incrementally decreased for WT+ADAMTS13, WT, and ADAMTS13-/- mice ( P<0.05), whereas infarct size incrementally increased ( P<0.05). CONCLUSIONS: Mechanistic information on microvascular no-reflow is possible by combining perfusion and molecular imaging. In reperfused myocardial infarction, excess endothelial-associated VWF and secondary platelet adhesion in the risk area microcirculation contribute to impaired reflow and are modifiable.