Changes in P-selectin expression on cardiac microvessels in blood-perfused rat hearts subjected to ischemia-reperfusion

Fucoidan-based micelles as P-selectin targeted carriers for synergistic treatment of acute kidney injury

Acute kidney injury (AKI) is a life-threatening disease without effective treatment. The utilization of curcumin (Cur) for the treatment of AKI is still facing challenges due to its poor water-solubility and low bioavailability. Herein, kidney-targeted octenyl succinic anhydride-grafted fucoidan loaded with Cur (OSA-Fucoidan/Cur) was fabricated for synergistic treatment of AKI. It was found that OSA-Fucoidan/Cur micelles had a sustained drug release behavior and excellent physicochemical stability. Cellular uptake studies demonstrated that the specific binding between fucoidan and P-selectin overexpressed on H2O2-stimulated HUVECs contributed to the higher internalization of OSA-Fucoidan/Cur micelles by the cells. In addition, OSA-Fucoidan micelles exhibited an ideal kidney-targeted characteristic in lipopolysaccharide (LPS)-induced AKI mice. In vivo studies showed that the combination of Cur and OSA-Fucoidan endowed the OSA-Fucoidan/Cur micelles with synergistically anti-inflammatory and antioxidant abilities, thereby largely enhancing the therapeutic efficacy of AKI. Therefore, OSA-Fucoidan/Cur micelles may represent a potential kidney-targeted nanomedicine for effective treatment of AKI.

Molecular Ultrasound Imaging

In the last decade, molecular ultrasound imaging has been rapidly progressing. It has proven promising to diagnose angiogenesis, inflammation, and thrombosis, and many intravascular targets, such as VEGFR2, integrins, and selectins, have been successfully visualized in vivo. Furthermore, pre-clinical studies demonstrated that molecular ultrasound increased sensitivity and specificity in disease detection, classification, and therapy response monitoring compared to current clinically applied ultrasound technologies. Several techniques were developed to detect target-bound microbubbles comprising sensitive particle acoustic quantification (SPAQ), destruction-replenishment analysis, and dwelling time assessment. Moreover, some groups tried to assess microbubble binding by a change in their echogenicity after target binding. These techniques can be complemented by radiation force ultrasound improving target binding by pushing microbubbles to vessel walls. Two targeted microbubble formulations are already in clinical trials for tumor detection and liver lesion characterization, and further clinical scale targeted microbubbles are prepared for clinical translation. The recent enormous progress in the field of molecular ultrasound imaging is summarized in this review article by introducing the most relevant detection technologies, concepts for targeted nano- and micro-bubbles, as well as their applications to characterize various diseases. Finally, progress in clinical translation is highlighted, and roadblocks are discussed that currently slow the clinical translation.

The Coronary Circulation as a Target of Cardioprotection

The atherosclerotic coronary vasculature is not only the culprit but also a victim of myocardial ischemia/reperfusion injury. Manifestations of such injury are increased vascular permeability and edema, endothelial dysfunction and impaired vasomotion, microembolization of atherothrombotic debris, stasis with intravascular cell aggregates, and finally, in its most severe form, capillary destruction with hemorrhage. In animal experiments, local and remote ischemic pre- and postconditioning not only reduce infarct size but also these manifestations of coronary vascular injury, as do drugs which recruit signal transduction steps of conditioning. Clinically, no-reflow is frequently seen after interventional reperfusion, and it carries an adverse prognosis. The translation of cardioprotective interventions to clinical practice has been difficult to date. Only 4 drugs (brain natriuretic peptide, exenatide, metoprolol, and esmolol) stand unchallenged to date in reducing infarct size in patients with reperfused acute myocardial infarction; unfortunately, for these drugs, no information on their impact on the ischemic/reperfused coronary circulation is available.

Cell surface glycoengineering improves selectin-mediated adhesion of mesenchymal stem cells (MSCs) and cardiosphere-derived cells (CDCs): Pilot validation in porcine ischemia-reperfusion model

Promising results are emerging in clinical trials focused on stem cell therapy for cardiology applications. However, the low homing and engraftment of the injected cells to target tissue continues to be a problem. Cellular glycoengineering can address this limitation by enabling the targeting of stem cells to sites of vascular injury/inflammation. Two such glycoengineering methods are presented here: i. The non-covalent incorporation of a P-selectin glycoprotein ligand-1 (PSGL-1) mimetic 19Fc[FUT7(+)] via lipid-protein G fusion intermediates that intercalate onto the cell surface, and ii. Over-expression of the α(1,3)fucosyltransferse FUT7 in cells. Results demonstrate the efficient coupling of 19Fc[FUT7(+)] onto both cardiosphere-derived cells (CDCs) and mesenchymal stem cells (MSCs), with coupling being more efficient when using protein G fused to single-tailed palmitic acid rather than double-tailed DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine). This non-covalent cellular modification was mild since cell proliferation and stem-cell marker expression was unaltered. Whereas coupling using 19Fc[FUT7(+)] enhanced cell capture on recombinant P-selectin or CHO-P cell surfaces, α(1,3)fucosylation was necessary for robust binding to E-selectin and inflamed endothelial cells under shear. Pilot studies confirm the safety and homing efficacy of the modified stem cells to sites of ischemia-reperfusion in the porcine heart. Overall, glycoengineering with physiological selectin-ligands may enhance stem cell engraftment.

Detection of antecedent myocardial ischemia with multiselectin molecular imaging

OBJECTIVES

Our aim was to develop an echocardiographic molecular imaging approach for detecting recent myocardial ischemia by using recombinant P-selectin glycoprotein ligand (PSGL)-1 as a targeting ligand, which is a feasible approach for human use.

BACKGROUND

Ischemic memory imaging using human PSGL-1 as a targeting moiety may extend the time window for postischemic detection by targeting the early (P-selectin) and late (E-selectin) endothelial ischemic response.

METHODS

Lipid microbubbles bearing recombinant human PSGL-1 (MB(YSPSL)) or P-selectin antibody (MB(Ab)) were prepared. Targeted attachment was evaluated by using flow chamber and intravital microscopy. In vivo ultrasound molecular imaging was first performed in the hindlimb in wild-type and P-selectin-deficient (P(-/-)) mice 45 to 360 min after brief ischemia-reperfusion injury. Myocardial contrast echocardiography molecular imaging was performed 1.5, 3, 6, and 18 h after brief left anterior descending coronary artery ischemia-reperfusion.

RESULTS

Microbubble attachment to P-selectin-immunoglobulin G fusion protein in flow chamber experiments (shear stress 0.5 to 8.0 dyne/cm(2)) and to activated venular endothelium on intravital microscopy were similar for MB(Ab) and MB(YSPSL). Intense enhancement was seen for MB(Ab) and MB(YSPSL) in postischemic muscle and was more stable over time for MB(YSPSL). On myocardial contrast echocardiography, both MB(YSPSL) and MB(Ab) produced similar signal enhancement at 90 min and 3 h after ischemia, which spatially correlated with the postischemic risk area. Signal significantly decreased but was still present at 6 to 18 h.

CONCLUSIONS

Echocardiographic molecular imaging with a human multi-selectin-targeted contrast agent bearing recombinant human PSGL-1 can detect myocardial ischemia hours after resolution. This approach may potentially be used for rapid bedside evaluation of patients with recent chest pain.

Selectins and Associated Adhesion Proteins in Inflammatory disorders

Inflammation is defined as the normal response of living tissue to injury or infection. It is important to emphasize two components of this definition. First, that inflammation is a normal response and, as such, is expected to occur when tissue is damaged. Infact, if injured tissue does not exhibit signs of inflammation this would be considered abnormal and wounds and infections would never heal without inflammation. Secondly, inflammation occurs in living tissue, hence there is need for an adequate blood supply to the tissues in order to exhibit an inflammatory response. The inflammatory response may be triggered by mechanical injury, chemical toxins, and invasion by microorganisms, and hypersensitivity reactions. Three major events occur during the inflammatory response: the blood supply to the affected area is increased substantially, capillary permeability is increased, and leucocytes migrate from the capillary vessels into the surrounding interstitial spaces to the site of inflammation or injury. The inflammatory response represents a complex biological and biochemical process involving cells of the immune system and a plethora of biological mediators. Cell-to-cell communication molecules such as cytokines play an extremely important role in mediating the process of inflammation. Inflammation and platelet activation are critical phenomena in the setting of acute coronary syndromes. An extensive exposition of this complex phenomenon is beyond the scope of this article (Rankin 2004).

Radiolabeled fucoidan as a p-selectin targeting agent for in vivo imaging of platelet-rich thrombus and endothelial activation

P-selectin expression is involved in the pathophysiology of biologically active arterial thrombus and endothelial activation after a transient ischemic event. Fucoidan is a polysaccharidic ligand of P-selectin, with a nanomolar affinity. In the present study, we propose a new approach of P-selectin molecular imaging based on radiolabeled fucoidan.

METHODS

Two kinds of experimental models were selected to evaluate the ability of radiolabeled fucoidan to detect P-selectin expression: platelet-rich arterial thrombi (vegetations of infective endocarditis and arterial mural thrombus) and myocardial ischemia-reperfusion. These 2 settings were chosen because they were clinically relevant, and both were associated with an important overexpression of platelet and endothelial P-selectin, respectively.

RESULTS

(99m)Tc-fucoidan SPECT was able to detect the presence of platelet-rich arterial thrombi in all animals, with a median target-to-background ratio of 5.2 in vegetations of endocarditis and 3.6 in mural aneurysmal thrombus, and to detect a persistent endothelial activation at 2 h after reperfusion. In this latter model, the magnitude of the signal was correlated with the extent of myocardium that underwent transient ischemia. The sensitivity of selectivity of the uptake and retention of (99m)Tc-fucoidan in both settings was excellent.

CONCLUSION

This study supports (99m)Tc-fucoidan as a relevant imaging agent for in vivo detection of biologic activities associated with P-selectin overexpression, such as arterial thrombus and ischemic memory. Given the reported wide availability at a low cost, and its low toxicity, fucoidan seems to overcome some of the limitations of previous P-selectin-targeted imaging agents.

Randomized transcoronary delivery of CD34(+) cells with perfusion versus stop-flow method in patients with recent myocardial infarction: Early cardiac retention of ⁹⁹(m)Tc-labeled cells activity

BACKGROUND

For transcoronary progenitor cells' administration, injections under flow arrest (over-the-wire balloon technique, OTW) are used universally despite lack of evidence for being required for cell delivery or being effective in stimulating myocardial engraftment. Flow-mediated endothelial rolling is mandatory for subsequent cell adhesion and extravasation.

METHODS

To optimize cell directing toward the coronary endothelium under maintained flow, the authors developed a cell-delivery side-holed perfusion catheter (PC). Thirty-four patients (36-69 years, 30 men) with primary stent-assisted angioplasty-treated anterior MI (peak TnI 151 [53-356]ng/dL, mean[range]) were randomly assigned to OTW or PC autologous ⁹⁹Tc-extametazime-labeled bone marrow CD34(+) cells (4.34 [0.92-7.54] × 10⁶) administration at 6-14 days after pPCI (LVEF 37.1 [24-44]%). Myocardial perfusion (⁹⁹(m)Tc-MIBI) and labeled cells' activity were evaluated (SPECT) at, respectively, 36-48 h prior to and 60 min after delivery.

RESULTS

In contrast to OTW coronary occlusions, no intolerance or ventricular arrhythmia occurred with PC cells' administration (P < .001). One hour after delivery, 4.86 [1.7-7.6]% and 5.05 [2.2-9.9]% activity was detected in the myocardium (OTW and PC, respectively, P = .84). Labeled cell activity was clearly limited to the (viable) peri-infarct zone in 88% patients, indicating that the infarct core zone may be largely inaccessible to transcoronary-administered cells.

CONCLUSIONS

Irrespective of the transcoronary delivery method, only ≈ 5% of native (i.e., non-engineered) CD34(+) cells spontaneously home to the injured myocardium, and cell retention occurs preferentially in the viable peri-infarct zone. Although the efficacy of cell delivery is not increased with the perfusion method, by avoiding provoking ischemic episodes PC offers a rational alternative to the OTW delivery.

Upregulation of coronary endothelial P-selectin in a monkey heart ischemia reperfusion model

The design of targeted ultrasound contrast agents for molecular imaging of myocardial ischemia-reperfusion (IR) requires the availability of an adequate in vivo model in a species in which cross reactivity with the target occurs. P-selectin (Psel) is an activation-dependent endothelial receptor that supports rapid and reversible cell adhesion in a flowing system. Together with E- and L-selectins it constitutes the selectin family of adhesion molecules. We investigated the myocardial expression of selectins in a closed chest minimally invasive monkey myocardial IR model. Catheter-based occlusion (30-50 min) followed by reperfusion (3 or 5 h) of left anterior descending artery (LAD) was performed in anesthetised monkeys. At the end of each procedure animals were killed, and their hearts were excised. The tissues were analyzed immunohistochemically using an anti-human Psel antibody (AK-6 clone) that cross reacts with rhesus monkey. Histopathological features confirm the presence of IR injuries in myocardial tissues. There was significant increase in the Psel expression in vessels from the IR areas. However, significantly higher Psel immunoreactivity was also seen in areas which are distant from IR injuries.

Molecular imaging with contrast enhanced ultrasound

Noninvasive cardiovascular imaging techniques are well-established for studying cardiovascular anatomy and physiology. Over the past decade contrast enhanced imaging techniques have been developed that are also able to characterize the molecular constituents of cardiovascular disease. In this regard, microbubble- and ultrasound-based techniques have the ability to assess a broad range of molecular components of cardiovascular pathology such as inflammation, recent ischemia, atherosclerosis, acute transplant rejection, angiogenesis, and thrombosis. The advantages of ultrasound- and microbubble-based approach include the ability to assess multiple molecular disease markers without exposure to ionizing radiation or prolonged imaging protocols. This review highlights the development of microbubble-based molecular imaging, describes successful experimental conditions in which they have been studied, and postulates the importance of translating this technique into the clinical practice.

Molecular imaging of myocardial and vascular disorders with ultrasound

Methods for noninvasive imaging of specific disease-related molecular changes are being developed in order to expand and improve diagnostic capabilities and to enhance therapeutic decision making in the clinical setting. These new techniques have also started to be incorporated into research programs in order to better characterize pathophysiology or evaluate treatment efficacy. Molecular imaging with contrast-enhanced ultrasound relies on the detection of the acoustic signal produced by either microbubbles or other acoustically active particulate agents that are targeted to sites of disease. This review describes the progress that has been made in the development and testing of methods for contrast ultrasound molecular imaging of cardiovascular disease. Specifically, topics that will be addressed include: 1) the bioengineering and detection schemes for targeted probes; 2) specific disease processes (myocardial ischemia, atherosclerosis, and transplant rejection) where molecular imaging may play a role; and 3) the potential role of ultrasound as a molecular imaging technique.

Contrast ultrasound molecular imaging of inflammation in cardiovascular disease

The cellular immune response plays an important role in almost every major form of cardiovascular disease. The ability to image the key aspects of the immune response in the clinical setting could be used to improve diagnostic information, to provide important prognostic or risk information, and to customize therapy according to disease phenotype. Accordingly, targeted imaging probes for assessing inflammation have been developed for essentially all forms of medical imaging. Molecular imaging of inflammation with contrast ultrasound relies on the detection of targeted microbubble or other gas-filled particle contrast agents. These agents are confined to the vascular space and, hence, have been targeted to either activated leucocytes or endothelial cell adhesion molecules that are upregulated in inflammation and mediate leucocyte recruitment and adhesion. This review focuses on the inflammation-targeting strategies for ultrasound contrast agents and how they have been matched to cardiovascular disease states such as myocardial ischaemia, infarction, atherosclerosis, transplant rejection, and arteriogenesis.

Targeting VEGF-encapsulated immunoliposomes to MI heart improves vascularity and cardiac function

Recent attempts at rebuilding the myocardium using stem cells have yielded disappointing results. The lack of a supporting vasculature may, in part, explain these disappointing findings. However, concerns over possible side effects have hampered attempts at revascularizing the infarcted myocardium using systemic delivery of proangiogenic compounds. In this study, we develop the technology to enhance the morphology and function of postinfarct neovasculature. Previously, we have shown that the up-regulated expression of endothelial cell adhesion molecules in the myocardial infarction (MI) region provides a potential avenue for selectively targeting drugs to infarcted tissue. After treatment with anti-P-selectin-conjugated liposomes containing vascular endothelial growth factor (VEGF), changes in cardiac function and vasculature post-MI were quantified in a rat MI model. Targeted delivery of VEGF to post-MI tissue resulted in significant increase in fractional shortening and improved systolic function. These functional improvements were accompanied by a 21% increase in the number of anatomical vessels and a 74% increase in the number of perfused vessels in the MI region of treated animals. No significant improvements in cardiac function were observed in untreated, systemic VEGF-treated, nontargeted liposome-treated, or blank immunoliposome-treated animals. Targeted delivery of low doses of proangiogenic compounds to post-MI tissue results in significant improvements in cardiac function and vascular structure.

Molecular imaging of cardiovascular disease with contrast-enhanced ultrasonography

Techniques for noninvasive imaging of specific disease-related molecular changes are being developed to enhance diagnosis and therapeutic decision making in the clinical setting, and to facilitate research efforts. Molecular imaging with contrast-enhanced ultrasonography relies on the detection of the acoustic signal produced by microbubble or nanoparticle agents that are targeted to sites of disease. This Review describes the basis for ultrasound molecular imaging, the unique features of contrast agent behavior or detector performance in relation to clinical or research needs, and the progress that has been made to date in imaging key events in cardiovascular medicine, such as atherosclerosis, postischemic inflammation, angiogenesis, transplant rejection and thrombus formation.

Detection of recent myocardial ischaemia by molecular imaging of P-selectin with targeted contrast echocardiography

AIMS

We hypothesized that molecular imaging of endothelial P-selectin expression with targeted myocardial contrast echocardiography (MCE) could identify recently ischaemic myocardium without infarction.

METHODS AND RESULTS

The microvascular behaviour of P-selectin-targeted (MB(p)) and control (MB(c)) microbubbles was assessed by intravital microscopy of the cremaster muscle in mice. Targeted MCE imaging with MB(p) and MB(c) was performed in mice after brief left anterior descending (LAD) occlusion and reperfusion and in open- and closed-chest controls. Regional wall motion and perfusion by MCE were assessed during occlusion and after reperfusion. On intravital microscopy, ischaemia-reperfusion produced a 10-fold increase (P < 0.01) in venular attachment for MB(p). Attachment for MB(c) was rare. With myocardial ischaemia-reperfusion, LAD occlusion produced hypoperfusion and wall motion abnormalities that resolved after 45 min of reperfusion. At 45 min, signal enhancement in the post-ischaemic region was four-fold greater (P < 0.05) for MB(p) vs. MB(c). MB(p) produced low-level enhancement in non-ischaemic myocardium in all open-chest animals, suggesting P-selectin expression from surgical cardiac exposure.

CONCLUSION

Molecular imaging of P-selectin with targeted MCE can identify the presence of recently ischaemic myocardium in the absence of necrosis and after resolution of hypoperfusion and post-ischaemic stunning. This technique can potentially provide a method for risk stratifying patients with acute chest pain.

Multi-cell agent-based simulation of the microvasculature to study the dynamics of circulating inflammatory cell trafficking

Leukocyte trafficking through the microcirculation and into tissues is central in angiogenesis, inflammation, and the immune response. Although the literature is rich with mechanistic detail describing molecular mediators of these processes, integration of signaling events and cell behaviors within a unified spatial and temporal framework at the multi-cell tissue-level is needed to achieve a fuller understanding. We have developed a novel computational framework that combines agent-based modeling (ABM) with a network flow analysis to study monocyte homing. A microvascular network architecture derived from mouse muscle was incorporated into the ABM. Each individual cell was represented by an individual agent in the simulation. The network flow model calculates hemodynamic parameters (blood flow rates, fluid shear stress, and hydrostatic pressures) throughout the simulated microvascular network. These are incorporated into the ABM to affect monocyte transit through the network and chemokine/cytokine concentrations. In turn, simulated monocytes respond to their local mechanical and biochemical environments and make behavioral decisions based on a rule set derived from independent literature. Simulated cell behaviors give rise to emergent leukocyte rolling, adhesion, and extravasation. Molecular knockout simulations were performed to validate the model, and predictions of monocyte adhesion, rolling, and extravasation show good agreement with the independently published corresponding mouse studies.

Myocardial ischemic memory imaging with molecular echocardiography

BACKGROUND

Diagnosing acute coronary syndrome in patients presenting with chest discomfort is a challenge. Because acute myocardial ischemia/reperfusion is associated with endothelial upregulation of leukocyte adhesion molecules, which persist even after ischemia has resolved, we hypothesized that microbubbles designed to adhere to endothelial selectins would permit echocardiographic identification of recently ischemic myocardium.

METHODS AND RESULTS

Lipid microbubbles (diameter, 3.3+/-1.7 microm) were synthesized. The selectin ligand sialyl Lewis(x) was conjugated to the microbubble surface (MB(sLex)). Control bubbles (MB(CTL)) bore surface Lewis(x) or sialyl Lewis(c). Intravital microscopy of mouse cremaster muscle was performed after intravenous injection of MB(sLex) (n=11) or MB(CTL) (n=9) with or without prior intrascrotal tumor necrosis factor-alpha. There was greater adhesion of MB(sLex) to inflamed versus noninflamed endothelium (P = 0.0081). Rats (n=12) underwent 15 minutes of anterior descending coronary artery occlusion. After 30 minutes and 1 hour of reperfusion, high-mechanical-index nonlinear echocardiographic imaging was performed in which single frames were acquired at 3.5 and 4 minutes after intravenous injection of MB(sLex) or MB(CTL). Video intensity at 4 minutes was subtracted from that at 3.5 minutes to derive target-specific acoustic signal. MB(sLex) caused greater opacification in postischemic versus nonischemic myocardium at both time points (P < or = 0.002). Immunostaining confirmed endothelial P-selectin expression in the ischemic bed.

CONCLUSIONS

Echocardiographic identification of recently ischemic myocardium is possible using ultrasound contrast agents targeted to selectins. This may offer a new approach to the more timely and precise diagnosis of acute coronary syndrome in patients presenting with chest pain of uncertain cardiac origin.