Low-density lipoprotein promotes microvascular thrombosis by enhancing von Willebrand factor self-association.

von Willebrand factor (VWF) mediates primary hemostasis and thrombosis in response to hydrodynamic forces. We previously showed that high shear promoted self-association of VWF into hyperadhesive strands, which can be attenuated by high-density lipoprotein (HDL) and apolipoprotein A-I. In this study, we show that low-density lipoprotein (LDL) binds VWF under shear and enhances self-association. Vortexing VWF in tubes resulted in its loss from the solution and deposition onto tube surfaces, which was prevented by HDL. At a stabilizing HDL concentration of 1.2 mg/mL, increasing concentrations of LDL progressively increased VWF loss, the effect correlating with the LDL-to-HDL ratio and not the absolute concentration of the lipoproteins. Similarly, HDL diminished deposition of VWF in a post-in-channel microfluidic device, whereas LDL increased both the rate and extent of strand deposition, with both purified VWF and plasma. Hypercholesterolemic human plasma also displayed accelerated VWF accumulation in the microfluidic device. The initial rate of accumulation correlated linearly with the LDL-to-HDL ratio. In Adamts13-/- and Adamts13-/-LDLR-/- mice, high LDL levels enhanced VWF and platelet adhesion to the myocardial microvasculature, reducing cardiac perfusion, impairing systolic function, and producing early signs of cardiomyopathy. In wild-type mice, high plasma LDL concentrations also increased the size and persistence of VWF-platelet thrombi in ionophore-treated mesenteric microvessels, exceeding the accumulation seen in similarly treated ADAMTS13-deficient mice that did not receive LDL infusion. We propose that targeting the interaction of VWF with itself and with LDL may improve the course of thrombotic microangiopathies, atherosclerosis, and other disorders with defective microvascular circulation.

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.

Changes in microvascular perfusion of heart and skeletal muscle in sheep around the time of birth.

NEW FINDINGS: What is the central question of this study? How does the microvascular perfusion of striated muscle change during the dynamic developmental period between the late gestation fetus and early neonate? What is the main finding and its importance? In both myocardium and skeletal muscle, perfusion of striated muscle is significantly reduced in the neonate compared to the late term fetus, but flow reserve is unchanged. The results suggest striated muscle capillary networks grow more slowly relative to the myofibres they nourish during the perinatal period. ABSTRACT: Microvascular perfusion of striated muscle is an important determinant of health throughout life. Birth is a transition with profound effects on the growth and function of striated muscle, but the regulation of microvascular perfusion around this transition is poorly understood. We used contrast-enhanced ultrasound perfusion imaging (CEUS) to study the perfusion of left ventricular myocardium and hindlimb biceps femoris, which are populations of muscle with different degrees of change in pre- to postnatal workloads and different capacities for postnatal proliferative growth. We studied separate groups of lambs in late gestation (135 days' gestational age; 92% of term) and shortly after birth (5 days' postnatal age). We used CEUS to quantify baseline perfusion, perfusion during hyperaemia induced by adenosine infusion (myocardium) or electrically stimulated unloaded exercise (skeletal muscle), flow reserve and oxygen delivery. We found heart-to-body weight ratio was greater in neonates than fetuses. Microvascular volume and overall perfusion were lower in neonates than fetuses in both muscle groups at baseline and with hyperaemia. Flux rate differed with muscle group, with myocardial flux being faster in neonates than fetuses, but skeletal muscle flux being slower. Oxygen delivery to skeletal muscle at baseline was lower in neonates than fetuses, but was not significantly different in myocardium. Flow reserve was not different between ages. Given the significant somatic growth, and the transition from hyperplastic to hypertrophic myocyte growth occurring in the perinatal period, we postulate that the primary driver of lower neonatal striated muscle perfusion is faster growth of myofibres than their associated capillary networks.

Contrast Echocardiography for Assessing Myocardial Perfusion.

PURPOSE OF REVIEW: Improvements in ultrasound methods for detecting microbubble ultrasound enhancing agents have led to an increase in the use of perfusion imaging with myocardial contrast echocardiography (MCE). This technique is now beginning to play an important role in specific clinical scenarios, which is the focus of this review. RECENT FINDINGS: MCE was originally conceived as a technique for detecting resting perfusion abnormalities related to ischemia at rest or during stress from coronary artery disease. More recently, MCE has increasingly been used in circumstances where the technique's ability to provide rapid, quantitative, or bedside assessment of perfusion is advantageous. Quantitative MCE is also increasingly being used as a research technique for evaluating pathobiology and therapy that involve changes in the myocardial microcirculation. While MCE was developed and validated decades ago, it is only now beginning to be used by an increasing number of clinicians due to improvements in imaging technology and recognition of specific situations where the technique is impactful.

Utilizing Contrast-Enhanced Ultrasonography with Phosphatidylserine Microbubbles to Detect Placental Inflammation in Rhesus Macaques.

The ability to comprehensively monitor physiological and detect pathophysiologic processes early during pregnancy can reduce maternal and fetal morbidity and mortality. Contrast-enhanced ultrasound (CEUS) is a non-invasive imaging technology that utilizes the acoustic detection of microbubbles to examine vascular spaces. Furthermore, microbubbles conjugated to specific compounds can focus studies on precise physiological pathways. We hypothesized that CEUS with phosphatidylserine microbubbles (MB-PS) could be employed to monitor placental inflammation. We tested this hypothesis in rhesus macaques (Macaca mulatta), a translational and relevant animal model of human placental health. As placental inflammation impacts many at-risk pregnancies, we performed CEUS with MB-PS in pregnant macaques fed a high-fat diet (e.g., a western-style diet, WSD) in the presence or absence of testosterone (T) to mimic the increased risk of polycystic ovary syndrome and subfertility. We have previously demonstrated a placental inflammation phenotype in this model, and, thus, we related the MB-PS CEUS signal intensity to placental inflammation markers: selectin p and angiopoietins. Testosterone exposure increased the MB-PS signal in the placental microcirculation on the maternal side compared to control animals. We found that T increased placental weight and decreased angiopoietin 2 (ANGPT2) immunoreactivity. Furthermore, a significant inverse correlation was found between MB-PS signal and ANGPT2. This indicated that CEUS with MB-PS can be used to monitor placental parameters. We propose that CEUS with MB-PS could aid in the identification of pregnancies at risk of placental vascular compromise.

Arterial Thrombotic Complications of Tyrosine Kinase Inhibitors.

Abnormal expression or function of several classes of kinases contribute to the development of many types of solid and hematologic malignancies. TKs (tyrosine kinases) in particular play a role in tumor growth, metastasis, neovascularization, suppression of immune surveillance, and drug resistance. TKIs (tyrosine kinase inhibitors) targeted to TKs such as BCR-ABL1, VEGF receptors, PDGF receptors, have transformed therapy of certain forms of cancer by providing excellent efficacy with relatively low adverse event rates. Yet some of these agents have been associated with high rates of vascular events, presumably from prothrombotic complications that result in myocardial infarction, stroke, and critical limb ischemia. This review describes the scope of the problem evidenced by clinical experience with some of the most commonly used TKIs, with a focus on TKIs targeted to the BCR-ABL1 (breakpoint cluster region-Abelson 1) translocation. We also discuss the potential mechanisms responsible for arterial thrombotic complications that could lead to mitigation strategies or unique TK targeting strategies to reduce adverse event rates without compromising efficacy.

Myocardial contrast echocardiography assessment of perfusion abnormalities in hypertrophic cardiomyopathy.

BACKGROUND: Perfusion defects during stress can occur in hypertrophic cardiomyopathy (HCM) from either structural or functional abnormalities of the coronary microcirculation. In this study, vasodilator stress myocardial contrast echocardiography (MCE) was used to quantify and spatially characterize hyperemic myocardial blood flow (MBF) deficits in HCM. METHODS: Regadenoson stress MCE was performed in patients with septal-variant HCM (n = 17) and healthy control subjects (n = 15). The presence and spatial distribution (transmural diffuse, patchy, subendocardial) of perfusion defects was determined by semiquantitative analysis. Kinetic analysis of time-intensity data was used to quantify MBF, microvascular flux rate (ß), and microvascular blood volume. In patients undergoing septal myectomy (n = 3), MCE was repeated > 1 years after surgery.  RESULTS: In HCM subjects, perfusion defects during stress occurred in the septum in 80%, and in non-hypertrophied regions in 40%. The majority of septal defects (83%) were patchy or subendocardial, while 67% of non-hypertrophied defects were transmural and diffuse. On quantitative analysis, hyperemic MBF was approximately 50% lower (p < 0.001) in the hypertrophied and non-hypertrophied regions of those with HCM compared to controls, largely based on an inability to augment ß, although hypertrophic regions also had blood volume deficits. There was no correlation between hyperemic MBF and either percent fibrosis on magnetic resonance imaging or outflow gradient, yet those with higher degrees of fibrosis (≥ 5%) or severe gradients all had low septal MBF during regadenoson. Substantial improvement in hyperemic MBF was observed in two of the three subjects undergoing myectomy, both of whom had severe pre-surgical outflow gradients at rest. CONCLUSION: Perfusion defects on vasodilator MCE are common in HCM, particularly in those with extensive fibrosis, but have a different spatial pattern for the hypertrophied and non-hypertrophied segments, likely reflecting different contributions of functional and structural abnormalities. Improvement in hyperemic perfusion is possible in those undergoing septal myectomy to relieve obstruction.  TRIAL REGISTRATION: ClinicalTrials.gov NCT02560467.

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.

Tyrosine Kinase Inhibitors in Leukemia and Cardiovascular Events: From Mechanism to Patient Care.

Targeted oncology therapies have revolutionized cancer treatment over the last decade and have resulted in improved prognosis for many patients. This advance has emanated from elucidation of pathways responsible for tumorigenesis followed by targeting of these pathways by specific molecules. Cardiovascular care has become an increasingly critical aspect of patient care in part because patients live longer, but also due to potential associated toxicities from these therapies. Because of the targeted nature of cancer therapies, cardiac and vascular side effects may additionally provide insights into the basic biology of vascular disease. We herein provide the example of tyrosine kinase inhibitors utilized in chronic myelogenous leukemia to illustrate this medical transformation. We describe the vascular considerations for the clinical care of chronic myelogenous leukemia patients as well as the emerging literature on mechanisms of toxicities of the individual tyrosine kinase inhibitors. We additionally postulate that basic insights into toxicities of novel cancer therapies may serve as a new platform for investigation in vascular biology and a new translational research opportunity in vascular medicine.

Perfusion Assessment in Critical Limb Ischemia: Principles for Understanding and the Development of Evidence and Evaluation of Devices: A Scientific Statement From the American Heart Association.

There are >12 million patients with peripheral artery disease in the United States. The most severe form of peripheral artery disease is critical limb ischemia (CLI). The diagnosis and management of CLI is often challenging. Ethnic differences in comorbidities and presentation of CLI exist. Compared with white patients, black and Hispanic patients have higher prevalence rates of diabetes mellitus and chronic renal disease and are more likely to present with gangrene, whereas white patients are more likely to present with ulcers and rest pain. A thorough evaluation of limb perfusion is important in the diagnosis of CLI because it can not only enable timely diagnosis but also reduce unnecessary invasive procedures in patients with adequate blood flow or among those with other causes for ulcers, including venous, neuropathic, or pressure changes. This scientific statement discusses the current tests and technologies for noninvasive assessment of limb perfusion, including the ankle-brachial index, toe-brachial index, and other perfusion technologies. In addition, limitations of the current technologies along with opportunities for improvement, research, and reducing disparities in health care for patients with CLI are discussed.

Increased endothelial shear stress improves insulin-stimulated vasodilatation in skeletal muscle.

KEY POINTS: It has been postulated that increased blood flow-associated shear stress on endothelial cells is an underlying mechanism by which physical activity enhances insulin-stimulated vasodilatation. This report provides evidence supporting the hypothesis that increased shear stress exerts insulin-sensitizing effects in the vasculature and this evidence is based on experiments in vitro in endothelial cells, ex vivo in isolated arterioles and in vivo in humans. Given the recognition that vascular insulin signalling, and associated enhanced microvascular perfusion, contributes to glycaemic control and maintenance of vascular health, strategies that stimulate an increase in limb blood flow and shear stress have the potential to have profound metabolic and vascular benefits mediated by improvements in endothelial insulin sensitivity. ABSTRACT: The vasodilator actions of insulin contribute to glucose uptake by skeletal muscle, and previous studies have demonstrated that acute and chronic physical activity improves insulin-stimulated vasodilatation and glucose uptake. Because this effect of exercise primarily manifests in vascular beds highly perfused during exercise, it has been postulated that increased blood flow-associated shear stress on endothelial cells is an underlying mechanism by which physical activity enhances insulin-stimulated vasodilatation. Accordingly, herein we tested the hypothesis that increased shear stress, in the absence of muscle contraction, can acutely render the vascular endothelium more insulin-responsive. To test this hypothesis, complementary experiments were conducted using (1) cultured endothelial cells, (2) isolated and pressurized skeletal muscle arterioles from swine, and (3) humans. In cultured endothelial cells, 1 h of increased shear stress from 3 to 20 dynes cm-2 caused a significant shift in insulin signalling characterized by greater activation of eNOS relative to MAPK. Similarly, isolated arterioles exposed to 1 h of intraluminal shear stress (20 dynes cm-2 ) subsequently exhibited greater insulin-induced vasodilatation compared to arterioles kept under no-flow conditions. Finally, we found in humans that increased leg blood flow induced by unilateral limb heating for 1 h subsequently augmented insulin-stimulated popliteal artery blood flow and muscle perfusion. In aggregate, these findings across models (cells, isolated arterioles and humans) support the hypothesis that elevated shear stress causes the vascular endothelium to become more insulin-responsive and thus are consistent with the notion that shear stress may be a principal mechanism by which physical activity enhances insulin-stimulated vasodilatation.

Maternal high-fat diet reversal improves placental hemodynamics in a nonhuman primate model of diet-induced obesity.

BACKGROUND: In a Japanese macaque model of diet-induced obesity, we have previously demonstrated that consumption of a high-fat, "Western-style" diet (WSD) is associated with placental dysfunction and adverse pregnancy outcomes, independent of an obese maternal phenotype. Specifically, we have reported decreased uterine placental blood flow and increased inflammation with maternal WSD consumption. We also previously investigated the use of a promising therapeutic intervention that mitigated the adverse placental effects of a WSD but had unexpected detrimental effects on fetal pancreatic development. Thus, the objective of the current study was to determine whether simple preconception diet reversal (REV) would improve placental function. METHODS: Female Japanese macaques were divided into three groups: REV animals (n = 5) were switched from a chronic WSD (36% fat) to a low fat, CON diet (14% fat) prior to conception and throughout pregnancy. The CON (n = 6) and WSD (n = 6) cohorts were maintained on their respective diets throughout pregnancy. Maternal body weight and composition were regularly assessed and advanced noninvasive imaging was performed at midgestation (gestational day 90, G90, or 0.5 of gestation, where full term is G175), and G129, 1 day prior to C-section delivery at G130 (0.75 of gestation). Imaging studies comprised Doppler ultrasound (US), contrast-enhanced US, and dynamic contrast-enhanced magnetic resonance imaging to assess uteroplacental hemodynamics and maternal-side placental perfusion. RESULTS: Dietary intervention resulted in significant maternal weight loss prior to pregnancy, and improved lean to fat mass ratio. By advanced imaging we demonstrated that a chronic WSD led to decreased blood flow velocity in the intervillous space, delayed blood flow transfer through the maternal spiral arteries, and reduced total placental blood flow compared to CON fed animals. Dietary reversal ameliorated these concerning derangements, restoring these hemodynamic parameters to CON levels. CONCLUSIONS: Preconception dietary modification has beneficial effects on the maternal metabolic phenotype, and results in improved placental hemodynamics.

Platelets and von Willebrand factor in atherogenesis.

The role of platelet adhesion, activation, and aggregation in acute atherothrombotic events such as myocardial infarction and stroke is well established. There is increasing evidence that platelet-endothelial interactions also contribute to early atherosclerotic plaque initiation and growth. Through these interactions, platelet-derived factors can contribute to the proinflammatory and mitogenic status of resident mural cells. Among the many putative mechanisms for platelet-endothelial interactions, increased endothelial-associated von Willebrand factor, particularly in a multimerized form, which interacts with platelet glycoproteins and integrins, is a major factor and represents a therapeutic target in early atherogenesis.

Ultrasound Molecular Imaging: Principles and Applications in Cardiovascular Medicine.

PURPOSE OF REVIEW: Non-invasive molecular imaging is currently used as a research technique to better understand disease pathophysiology. There are also many potential clinical applications where molecular imaging may provide unique information that allows either earlier or more definitive diagnosis, or can guide precision medicine-based decisions on therapy. Contrast-enhanced ultrasound (CEU) with targeted microbubble contrast agents is one such technique that has been developed that has the unique properties of providing rapid information and revealing information only on events that occur within the vascular space. RECENT FINDINGS: CEU molecular probes have been developed for a wide variety of disease states including atherosclerosis, vascular inflammation, thrombosis, tumor neovascularization, and ischemic injury. While the technique has not yet been adapted to clinical use, it has been used to reveal pathological processes, to identify new therapeutic targets, and to test the efficacy of novel treatments. This review will explore the physical basis for CEU molecular imaging, its strengths and limitations compared to other molecular imaging modalities, and the pre-clinical translational research experience.

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.

Endothelial vascular cell adhesion molecule 1 is a marker for high-risk carotid plaques and target for ultrasound molecular imaging.

BACKGROUND: Molecular imaging of carotid plaque vulnerability to atheroembolic events is likely to lead to improvements in selection of patients for carotid endarterectomy (CEA). The aims of this study were to assess the relative value of endothelial inflammatory markers for this application and to develop molecular ultrasound contrast agents for their imaging. METHODS: Human CEA specimens were obtained prospectively from asymptomatic (30) and symptomatic (30) patients. Plaques were assessed by semiquantitative immunohistochemistry for vascular cell adhesion molecule 1 (VCAM-1), lectin-like oxidized low-density lipoprotein receptor 1, P-selectin, and von Willebrand factor. Established small peptide ligands to each of these targets were then synthesized and covalently conjugated to the surface of lipid-shelled microbubble ultrasound contrast agents, which were then evaluated in a flow chamber for binding kinetics to activated human aortic endothelial cells under variable shear conditions. RESULTS: Expression of VCAM-1 on the endothelium of CEA specimens from symptomatic patients was 2.4-fold greater than that from asymptomatic patients (P < .01). Expression was not significantly different between groups for P-selectin (P = .43), von Willebrand factor (P = .59), or lectin-like oxidized low-density lipoprotein receptor 1 (P = .99). Although most plaques from asymptomatic patients displayed low VCAM-1 expression, approximately one in five expressed high VCAM-1 similar to plaques from symptomatic patients. In vitro flow chamber experiments demonstrated that VCAM-1-targeted microbubbles bind cells that express VCAM-1, even under high-shear conditions that approximate those found in human carotid arteries, whereas binding efficiency was lower for the other agents. CONCLUSIONS: VCAM-1 displays significantly higher expression on high-risk (symptomatic) vs low-risk (asymptomatic) carotid plaques. Ultrasound contrast agents bearing ligands for VCAM-1 can sustain high-shear attachment and may be useful for identifying patients in whom more aggressive treatment is warranted.

Skeletal and myocardial microvascular blood flow in hydroxycarbamide-treated patients with sickle cell disease.

In sickle cell disease (SCD), abnormal microvascular function combined with chronic anaemia predisposes patients to perfusion-demand mismatch. We hypothesized that skeletal muscle and myocardial perfusion, normalized to the degree of anaemia, is reduced at basal-state compared to controls, and that this defect is ameliorated by hydroxycarbamide (HC; also termed hydroxyurea) therapy. Twenty-one SCD patients, of whom 15 were treated with HC, and 27 controls underwent contrast-enhanced ultrasound (CEU) perfusion imaging of the forearm as well as the myocardium. HC treatment was associated with lower white cell and reticulocyte counts, and higher fetal haemoglobin and total haemoglobin levels. When corrected for the degree of anaemia in SCD patients, skeletal flow in HC-treated patients was significantly higher than in untreated SCD patients (217·7 ± 125·4 vs. 85·9 ± 40·2, P = 0·018). Similarly, when normalized for both anaemia and increased myocardial work, resting myocardial perfusion was also significantly higher in HC-treated patients compared with untreated SCD patients (0·53 ± 0·47 vs. 0·13 ± 0·07, P = 0·028). Haemoglobin F (HbF) levels correlated with skeletal muscle microvascular flow (r = 0·55, P = 0·01). In conclusion, patients with SCD not on HC therapy have resting flow deficits in both skeletal muscle and myocardial flow. HC therapy normalizes flow and there is a direct correlation with HbF levels. Clinical trial registration ClinicalTrials.gov Identifier: NCT01602809; https://clinicaltrials.gov/ct2/show/NCT01602809?term=sACHDEV&rank=9.