Procedural and 1-year clinical outcomes of orbital atherectomy for treatment of coronary in-stent restenosis: A single-center, retrospective study.

OBJECTIVES: We evaluated the procedural and 1-year clinical outcomes of orbital atherectomy (OA) for treatment of coronary in-stent restenosis (ISR). BACKGROUND: The optimal treatment for ISR remains uncertain. While rotational and laser atherectomy have been used as neointimal debulking techniques for ISR, there have been few reports on OA for ISR. METHODS: This is a retrospective observational study of consecutive patients who underwent percutaneous coronary intervention (PCI) for ISR with OA in Mount Sinai catheterization laboratory between November 2013 and January 2018. Procedural success was defined as angiographic success without in-hospital major adverse cardiac events (MACE; the composite of all-cause death, myocardial infarction [MI], or target vessel revascularization). Clinical outcomes were assessed at 1 month and 12 months postprocedure. RESULTS: A total of 87 patients were included in the study. All 87 patients were treated with OA, after which 49 (56.3%) patients also received new drug-eluting stents. Angiographic success was achieved in 87 (100%) patients and procedural success was achieved in 79 (90.8%) patients. In-hospital MACE occurred in 8 (9.2%) patients, all due to periprocedural non-Q-wave MI. Acute lumen gain was 1.19 ± 0.57 mm after OA plus balloon angioplasty and 1.75 ± 0.50 mm after stent placement. MACE within 1 year occurred in 17 (19.5%) patients. CONCLUSIONS: OA for ISR was performed with favorable procedural and 1-year clinical outcomes. Randomized trials are warranted to determine whether OA improves the poor prognosis of patients with ISR treated without debulking.

Molecular Imaging of Apoptosis in Atherosclerosis by Targeting Cell Membrane Phospholipid Asymmetry.

BACKGROUND: Apoptosis in atherosclerotic lesions contributes to plaque vulnerability by lipid core enlargement and fibrous cap attenuation. Apoptosis is associated with exteriorization of phosphatidylserine (PS) and phosphatidylethanolamine (PE) on the cell membrane. Although PS-avid radiolabeled annexin-V has been employed for molecular imaging of high-risk plaques, PE-targeted imaging in atherosclerosis has not been studied. OBJECTIVES: This study sought to evaluate the feasibility of molecular imaging with PE-avid radiolabeled duramycin in experimental atherosclerotic lesions in a rabbit model and compare duramycin targeting with radiolabeled annexin-V. METHODS: Of the 27 rabbits, 21 were fed high-cholesterol, high-fat diet for 16 weeks. Nine of the 21 rabbits received 99mTc-duramycin (test group), 6 received 99mTc-linear duramycin (duramycin without PE-binding capability, negative radiotracer control group), and 6 received 99mTc-annexin-V for radionuclide imaging. The remaining normal chow-fed 6 animals (disease control group) received 99mTc-duramycin. In vivo microSPECT/microCT imaging was performed, and the aortas were explanted for ex vivo imaging and for histological characterization of atherosclerosis. RESULTS: A significantly higher duramycin uptake was observed in the test group compared with that of disease control and negative radiotracer control animals; duramycin uptake was also significantly higher than the annexin-V uptake. Quantitative duramycin uptake, represented as the square root of percent injected dose per cm (√ID/cm) of abdominal aorta was >2-fold higher in atherosclerotic lesions in test group (0.08 ± 0.01%) than in comparable regions of disease control animals (0.039 ± 0.0061%, p = 3.70·10-8). Mean annexin uptake (0.060 ± 0.010%) was significantly lower than duramycin (p = 0.001). Duramycin uptake corresponded to the lesion severity and macrophage burden. The radiation burden to the kidneys was substantially lower with duramycin (0.49% ID/g) than annexin (5.48% ID/g; p = 4.00·10-4). CONCLUSIONS: Radiolabeled duramycin localizes in lipid-rich areas with high concentration of apoptotic macrophages in the experimental atherosclerosis model. Duramycin uptake in atherosclerotic lesions was significantly greater than annexin-V uptake and produced significantly lower radiation burden to nontarget organs.

Rat Model of Cardiotoxic Drug-Induced Cardiomyopathy.

Cardiotoxicity from cancer drugs remains a clinical problem. To find reliable markers of cardiotoxicity, animal models were proposed and potential new diagnostic markers have been actively investigated using these models. Here we describe our protocols, using male Sprague-Dawley rats, for inducing cardiomyopathy by single injection of high-dose doxorubicin (5-10 mg/kg) or multiple injections (2-4 times) of low-dose doxorubicin (2.5 mg/kg) with combined single injection of trastuzumab (10 mg/kg). The cardiotoxicity is evaluated by imaging modalities (echocardiography and nuclear imaging), serum troponin levels, and histopathological analyses.

Molecular Imaging of Apoptosis in Ischemia Reperfusion Injury With Radiolabeled Duramycin Targeting Phosphatidylethanolamine: Effective Target Uptake and Reduced Nontarget Organ Radiation Burden.

OBJECTIVES: The purpose of this study was to evaluate the feasibility of imaging apoptosis in experimental ischemia-reperfusion model by technetium-99m (99mTc)-labeled Duramycin, and compare it to an established tracer, 99mTc-labeled Annexin-V, which has a relative disadvantage of high radiation burden to nontarget organs. BACKGROUND: During apoptosis, the cell membrane phospholipids-phosphatidylserine (PS) and phosphatidylethanolamine (PE) are exposed and can be targeted by Annexin-V and Duramycin, respectively, for in vivo imaging. Identification of a reversible cell death process should permit therapeutic intervention to help reduce myocyte loss and left ventricle dysfunction. METHODS: In a 40-min left coronary artery ischemia-reperfusion model in 17 rabbits, 7 mCi of 99mTc-labeled Duramycin (n = 10), 99mTc-linear Duramycin (a negative tracer control; n = 3), or 99mTc-Annexin-V (a positive tracer-control; n = 4) were intravenously administered 30 min after reperfusion. Of the 10 Duramycin group animals, 4 animals were treated with an antiapoptotic agent, minocycline at the time of reperfusion. In vivo and ex vivo micro-single-photon emission computed tomography (µSPECT) and micro-computed tomography (µCT) imaging was performed 3 h after reperfusion, followed by quantitative assessment of tracer uptake and pathological characterization. Fluorescent Duramycin and Annexin-V were injected in 4 rats to visualize colocalization in infarct areas in a 40-min left coronary artery occlusion and 30-min reperfusion model. RESULTS: Intense uptake of Duramycin and Annexin-V was observed in the apical (infarcted) areas. The percent injected dose per gram uptake of Duramycin in apical region (0.751 ± 0.262%) was significantly higher than remote area in same animals (0.045 ± 0.029%; p < 0.01). Duramycin uptake was insignificantly lower than Annexin-V uptake (1.23 ± 0.304%; p > 0.01) but demonstrated substantially lower radiation burden to kidneys (0.358 ± 0.210% vs. 1.58 ± 0.316%, respectively; p < 0.001). Fluorescence studies with Duramycin and Annexin V showed colocalization in infarct areas. Minocycline treatment substantially resolved Duramycin uptake (0.354% ± 0.0624%; p < 0.01). CONCLUSIONS: Duramycin is similarly effective in imaging apoptotic cell death as Annexin-V with lower nontarget organ radiation. Clinical feasibility of apoptosis imaging with a PE-seeking tracer should be tested.

Cardioprotection by minocycline in a rabbit model of ischemia/reperfusion injury: Detection of cell death by in vivo 111In-GSAO SPECT.

BACKGROUND: Preclinical studies indicate that minocycline protects against myocardial ischemia/reperfusion injury. In these studies, minocycline was administered before ischemia, which can rarely occur in clinical practice. The current study aimed to evaluate cardioprotection by minocycline treatment upon reperfusion. METHODS: Rabbits were subjected to myocardial ischemia/reperfusion injury and received either intravenous minocycline (n = 8) or saline (n = 8) upon reperfusion. Cardiac cell death was assessed by in vivo micro-SPECT/CT after injection of Indium-111-labeled 4-(N-(S-glutathionylacetyl)amino) phenylarsonous acid (111In-GSAO). Thereafter, hearts were explanted for ex vivo imaging, γ-counting, and histopathological characterization. RESULTS: Myocardial damage was visualized by micro-SPECT/CT imaging. Quantitative GSAO uptake (expressed as percent injected dose per gram, %ID/g) in the area at risk was lower in minocycline-treated animals than that in saline-treated control animals (0.32 ± 0.13% vs 0.48 ± 0.15%, P = 0.04). TUNEL staining confirmed the reduction of cell death in minocycline-treated animals. CONCLUSIONS: This study demonstrates cardioprotection by minocycline in a clinically translatable protocol.

Cardioprotective Effects of HSP72 Administration on Ischemia-Reperfusion Injury.

BACKGROUND: Although early reperfusion is the most desirable intervention after ischemic myocardial insult, it may add to damage through oxidative stress. OBJECTIVES: This study investigated the cardioprotective effects of a single intravenous dose of heat shock protein-72 (HSP72) coupled to a single-chain variable fragment (Fv) of monoclonal antibody 3E10 (3E10Fv) in a rabbit ischemia-reperfusion model. The Fv facilitates rapid transport of HSP72 into cells, even with intact membranes. METHODS: A left coronary artery occlusion (40 min) reperfusion (3 h) model was used in 31 rabbits. Of these, 12 rabbits received the fusion protein (Fv-HSP72) intravenously. The remaining 19 control rabbits received a molar equivalent of 3E10Fv alone (n = 6), HSP72 alone (n = 6), or phosphate-buffered saline (n = 7). Serial echocardiographic examinations were performed to assess left ventricular function before and after reperfusion. Micro-single-photon emission computed tomography imaging of 99mTc-labeled annexin-V was performed with micro-computed tomography scanning to characterize apoptotic damage in vivo, followed by gamma counting of the excised myocardial specimens to quantify cell death. Histopathological characterization of the myocardial tissue and sequential cardiac troponin I measurements were also undertaken. RESULTS: Myocardial annexin-V uptake was 43% lower in the area at risk (p = 0.0003) in Fv-HSP72-treated rabbits compared with control animals receiving HSP72 or 3E10Fv alone. During reperfusion, troponin I release was 42% lower and the echocardiographic left ventricular ejection fraction 27% higher in the Fv-HSP72-treated group compared with control animals. Histopathological analyses confirmed penetration of 3E10Fv-containing molecules into cardiomyocytes in vivo, and treatment with Fv-HSP72 showed fewer apoptotic nuclei compared with control rabbits. CONCLUSIONS: Single-dose administration of Fv-HSP72 fusion protein at the time of reperfusion reduced myocardial apoptosis by almost one-half and improved left ventricular functional recovery after myocardial ischemia-reperfusion injury in rabbits. It might have potential to serve as an adjunct to early reperfusion in the management of myocardial infarction.

Noninvasive molecular imaging of cell death in myocardial infarction using 111In-GSAO.

Acute insult to the myocardium is associated with substantial loss of cardiomyocytes during the process of myocardial infarction. In this setting, apoptosis (programmed cell death) and necrosis may operate on a continuum. Because the latter is characterized by the loss of sarcolemmal integrity, we propose that an appropriately labeled tracer directed at a ubiquitously present intracellular moiety would allow non-invasive definition of cardiomyocyte necrosis. A trivalent arsenic peptide, GSAO (4-(N-(S-glutathionylacetyl)amino)phenylarsonous acid), is capable of binding to intracellular dithiol molecules such as HSP90 and filamin-A. Since GSAO is membrane impermeable and dithiol molecules abundantly present intracellularly, we propose that myocardial localization would represent sarcolemmal disruption or necrotic cell death. In rabbit and mouse models of myocardial infarction and post-infarct heart failure, we employed In-111-labelled GSAO for noninvasive radionuclide molecular imaging. (111)In-GSAO uptake was observed within the regions of apoptosis seeking agent- (99m)Tc-Annexin A5 uptake, suggesting the colocalization of apoptotic and necrotic cell death processes.

2-deoxy-2-[18F]fluoro-D-mannose positron emission tomography imaging in atherosclerosis.

Progressive inflammation in atherosclerotic plaques is associated with increasing risk of plaque rupture. Molecular imaging of activated macrophages with 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) has been proposed for identification of patients at higher risk for acute vascular events. Because mannose is an isomer of glucose that is taken up by macrophages through glucose transporters and because mannose receptors are expressed on a subset of the macrophage population in high-risk plaques, we applied (18)F-labeled mannose (2-deoxy-2-[(18)F]fluoro-D-mannose, [(18)F]FDM) for targeting of plaque inflammation. Here, we describe comparable uptake of [(18)F]FDM and [(18)F]FDG in atherosclerotic lesions in a rabbit model; [(18)F]FDM uptake was proportional to the plaque macrophage population. Our FDM competition studies in cultured cells with 2-deoxy-2-[(14)C]carbon-D-glucose ([(14)C]2DG) support at least 35% higher [(18)F]FDM uptake by macrophages in cell experiments. We also demonstrate that FDM restricts binding of anti-mannose receptor antibody to macrophages by approximately 35% and that mannose receptor targeting may provide an additional avenue for imaging of plaque inflammation.

Labeling galectin-3 for the assessment of myocardial infarction in rats.

BACKGROUND: Galectin-3 is a ß-galactoside-binding lectin expressed in most of tissues in normal conditions and overexpressed in myocardium from early stages of heart failure (HF). It is an established biomarker associated with extracellular matrix (ECM) turnover during myocardial remodeling. The aim of this study is to test the ability of (123)I-galectin-3 (IG3) to assess cardiac remodeling in a model of myocardial infarction (MI) using imaging techniques. METHODS: Recombinant galectin-3 was labeled with iodine-123 and in vitro binding assays were conducted to test (123)I-galectin-3 ability to bind to ECM targets. For in vivo studies, a rat model of induced-MI was used. Animals were subjected to magnetic resonance and micro-SPETC/micro-CT imaging two (2 W-MI) or four (4 W-MI) weeks after MI. Sham rats were used as controls. Pharmacokinetic, biodistribution, and histological studies were also performed after intravenous administration of IG3. RESULTS: In vitro studies revealed that IG3 shows higher binding affinity (measured as counts per minute, cpm) (p < 0.05) to laminin (2.45 ± 1.67 cpm), fibronectin (4.72 ± 1.95 cpm), and collagen type I (1.88 ± 0.53 cpm) compared to bovine serum albumin (BSA) (0.88 ± 0.31 cpm). Myocardial quantitative IG3 uptake (%ID/g) was higher (p < 0.01) in the infarct of 2 W-MI rats (0.15 ± 0.04%) compared to control (0.05 ± 0.03%). IG3 infarct uptake correlates with the extent of scar (r s = 1, p = 0.017). Total collagen deposition in the infarct (percentage area) was higher (p < 0.0001) at 2 W-MI (24.2 ± 5.1%) and 4 W-MI (30.4 ± 7.5%) compared to control (1.9 ± 1.1%). However, thick collagen content in the infarct (square micrometer stained) was higher at 4 W-MI (20.5 ± 11.2 µm(2)) compared to control (4.7 ± 2.0 µm(2), p < 0.001) and 2 W-MI (10.6 ± 5.1 µm(2), p < 0.05). CONCLUSIONS: This study shows, although preliminary, enough data to consider IG3 as a potential contrast agent for imaging of myocardial interstitial changes in rats after MI. Labeling strategies need to be sought to improve in vivo IG3 imaging, and if proven, galectin-3 might be used as an imaging tool for the assessment and treatment of MI patients.

Synthesis of polymer-lipid nanoparticles for image-guided delivery of dual modality therapy.

For advanced treatment of diseases such as cancer, multicomponent, multifunctional nanoparticles hold great promise. In the current study we report the synthesis of a complex nanoparticle (NP) system with dual drug loading as well as diagnostic properties. To that aim we present a methodology where chemically modified poly(lactic-co-glycolic) acid (PLGA) polymer is formulated into a polymer-lipid NP that contains a cytotoxic drug doxorubicin (DOX) in the polymeric core and an anti-angiogenic drug sorafenib (SRF) in the lipidic corona. The NP core also contains gold nanocrystals (AuNCs) for imaging purposes and cyclodextrin molecules to maximize the DOX encapsulation in the NP core. In addition, a near-infrared (NIR) Cy7 dye was incorporated in the coating. To fabricate the NP we used a microfluidics-based technique that offers unique NP synthesis conditions, which allowed for encapsulation and fine-tuning of optimal ratios of all the NP components. NP phantoms could be visualized with computed tomography (CT) and near-infrared (NIR) fluorescence imaging. We observed timed release of the encapsulated drugs, with fast release of the corona drug SRF and delayed release of a core drug DOX. In tumor bearing mice intravenously administered NPs were found to accumulate at the tumor site by fluorescence imaging.

The impact of pressure overload on coronary vascular changes following myocardial infarction in rats.

This study investigates the impact of pressure overload on vascular changes after myocardial infarction (MI) in rats. To evaluate the effect of pressure overload, MI was induced in three groups: 1) left coronary artery ligation for 1 mo (MI-1m), 2) ischemia 30 min/reperfusion for 1 mo (I/R-1m), and 3) ischemia-reperfusion (I/R) was performed after pressure overload induced by aortic banding for 2 mo; 1 mo post-I/R, aortic constriction was released (Ab+I/R+DeAb). Heart function was assessed by echocardiography and in vivo hemodynamics. Resin casting and three-dimensional imaging with microcomputed tomography were used to characterize changes in coronary vasculature. TTC (triphenyltetrazohum chloride) staining and Masson's Trichrome were conducted in parallel experiments. In normal rats, MI induced by I/R and permanent occlusion was transmural or subendocardial. Occluded arterial branches vanished in MI-1m rats. A short residual tail was retained, distal to the occluded site in the ischemic area in I/R-1m hearts. Vascular pathological changes in transmural MI mostly occurred in ischemic areas and remote vasculature remained normal. In pressure overloaded rats, I/R injury induced a sub-MI in which ischemia was transmural, but myocardium in the involved area had survived. The ischemic arterial branches were preserved even though the capillaries were significantly diminished and the pathological changes were extended to remote areas, characterized by fibrosis, atrial thrombus, and pulmonary edema in the Ab+I/R+DeAb group. Pressure overload could increase vascular tolerance to I/R injury, but also trigger severe global ventricular fibrosis and results in atrial thrombus and pulmonary edema.

Molecular imaging of human ACE-1 expression in transgenic rats.

OBJECTIVES: The aim of this study was to develop a molecular imaging strategy that can monitor myocardial angiotensin-converting enzyme (ACE)-1 upregulation as a function of progressive heart failure. BACKGROUND: High-affinity technetium-99m-labeled lisinopril (Tc-Lis) has been shown to specifically localize in tissues that express ACE in vivo, such as the lungs. Whether Tc-Lis can also detect upregulation of ACE in the heart, by external in vivo imaging, has not been established. METHODS: Twenty-one ACE-1 over-expressing transgenic (Tg) and 18 wild-type control rats were imaged using in vivo micro single-positron emission computed tomography (SPECT)-computed tomography (CT) at 10, 30, 60, and 120 min after Tc-Lis injection. A subgroup of rats received nonradiolabeled (cold) lisinopril before the Tc-Lis injection to evaluate nonspecific binding. After imaging, the rat myocardium was explanted, ex vivo images were acquired, and percent injected dose per gram gamma-well was counted, followed by an assessment of enzyme-linked immunosorbent assay-verified ACE activity and messenger ribonucleic acid expression. RESULTS: On micro SPECT-CT, myocardial ACE-1 uptake was best visualized in Tg rats at 120 min after Tc-Lis injection. The quantitative uptake of Tc-Lis in the myocardium was 5-fold higher in mutant Tg than in control rats at each time point after tracer injection. The percent injected dose per gram uptake was 0.74 ± 0.13 in Tg myocardium at 30 min and was reduced substantially to 0.034 ± 0.003% when pre-treated with cold lisinopril (p = 0.029). Enzyme activity assay showed a >30-fold higher level of ACE-1 activity in the myocardium of Tg rats than in controls. The ACE-1 messenger ribonucleic acid was quantified, and lisinopril was found to have no effect on ACE-1 gene expression. CONCLUSIONS: The Tc-Lis binds specifically to ACE, and the activity can be localized in Tg rat hearts that over-express human ACE-1 with a signal intensity that is sufficiently high to allow external imaging. Such a molecular imaging strategy may help identify susceptibility to heart failure and may allow optimization of pharmacologic intervention.

Effect of an antimicrobial agent on atherosclerotic plaques: assessment of metalloproteinase activity by molecular imaging.

OBJECTIVES: Technetium-99m-labeled matrix metalloproteinase inhibitor (MPI) was used for the noninvasive assessment of matrix metalloproteinase (MMP) activity in atherosclerotic plaques after minocycline (MC) intervention. BACKGROUND: MMP activity in atherosclerosis contributes to plaque instability. Some antimicrobial agents may attenuate MMP activity. METHODS: Atherosclerotic lesions were produced in 38 rabbits with a high cholesterol diet for 4 months; 5 groups of rabbits, in the fourth month, received fluvastatin (FS) (n = 6), low-dose MC (n = 7), high-dose MC (n = 7), a combination of low-dose MC and FS (n = 6), or no intervention (n = 12); 8 unmanipulated rabbits were used as disease controls. Micro-single-photon emission computed tomography imaging was performed in all animals after intravenous MPI administration, followed by pathologic characterization of the aorta. A cell culture study evaluated the effect of MC on MMP production by activated human monocytes. RESULTS: MPI uptake was visualized best in untreated atherosclerotic animals (percent injected dose per gram MPI uptake, 0.11 +/- 0.04%). MPI uptake was reduced in the FS (0.06 +/- 0.01%; p < 0.0001), high-dose MC (0.05 +/- 0.01%; p < 0.0001), and MC-FS (0.05 +/- 0.005%; p < 0.0001) groups. Low-dose MC did not resolve MPI uptake significantly (0.08 +/- 0.02; p = 0.167). There was no incremental benefit of the combination of MC and FS. MPI uptake showed a significant correlation with plaque MMP-2, and MMP-9 activity. MMP-9 release from tumor necrosis factor-alpha-activated macrophages was abrogated by incubation with MC. CONCLUSIONS: Molecular imaging of MMP activity in atherosclerotic plaque allows for the study of the efficacy of therapeutic interventions. MC administration resulted in substantial reduction in plaque MMP activity and histologically verified plaque stabilization. MC was found to be equally effective as FS.

Annexin A5 uptake in ischemic myocardium: demonstration of reversible phosphatidylserine externalization and feasibility of radionuclide imaging.

UNLABELLED: Ischemic insult to the myocardium is associated with cardiomyocyte apoptosis. Because apoptotic cell death is characterized by phosphatidylserine externalization on cell membrane and annexin-A5 (AA5) avidly binds to phosphatidylserine, we hypothesized that radiolabeled AA5 should be able to identify the regions of myocardial ischemia. METHODS: Models of brief myocardial ischemia by the occlusion of the coronary artery for 10 min (I-10) and reperfusion for 180 min (R-180) for the detection of phosphatidylserine exteriorization using (99m)Tc-labeled AA5 and gamma-imaging were produced in rabbits. (99m)Tc-AA5 uptake after brief ischemia was compared with an I-40/R-180 infarct model. Histologic characterization of both myocardial necrosis and apoptosis was performed in ischemia and infarct models. Phosphatidylserine exteriorization was also studied in a mouse model, and the dynamics and kinetics of phosphatidylserine exposure were assessed using unlabeled recombinant AA5 and AA5 labeled with biotin, Oregon Green, or Alexa 568. Appropriate controls were established. RESULTS: Phosphatidylserine exposure after ischemia in the rabbit heart could be detected by radionuclide imaging with (99m)Tc-AA5. Pathologic characterization of the explanted rabbit hearts did not show apoptosis or necrosis. Homogenization and ultracentrifugation of the ischemic myocardial tissue from rabbit hearts recovered two thirds of the radiolabeled AA5 from the cytoplasmic compartment. Murine experiments demonstrated that the cardiomyocytes expressed phosphatidylserine on their cell surface after an ischemic insult of 5 min. Phosphatidylserine exposure occurred continuously for at least 6 h after solitary ischemic insult. AA5 targeted the exposed phosphatidylserine on cardiomyocytes; AA5 was internalized into cytoplasmic vesicles within 10-30 min. Twenty-four hours after ischemia, cardiomyocytes with internalized AA5 had restored phosphatidylserine asymmetry of the sarcolemma, and no detectable phosphatidylserine remained on the cell surface. The preadministration of a pan-caspase inhibitor, zVAD-fmk, prevented phosphatidylserine exposure after ischemia. CONCLUSIONS: After a single episode of ischemia, cardiomyocytes express phosphatidylserine, which is amenable to targeting by AA5, for at least 6 h. Phosphatidylserine exposure is transient and internalized in cytoplasmic vesicles after AA5 binding, indicating the reversibility of the apoptotic process.

Small-animal SPECT and SPECT/CT: application in cardiovascular research.

Preclinical cardiovascular research using noninvasive radionuclide and hybrid imaging systems has been extensively developed in recent years. Single photon emission computed tomography (SPECT) is based on the molecular tracer principle and is an established tool in noninvasive imaging. SPECT uses gamma cameras and collimators to form projection data that are used to estimate (dynamic) 3-D tracer distributions in vivo. Recent developments in multipinhole collimation and advanced image reconstruction have led to sub-millimetre and sub-half-millimetre resolution SPECT in rats and mice, respectively. In this article we review applications of microSPECT in cardiovascular research in which information about the function and pathology of the myocardium, vessels and neurons is obtained. We give examples on how diagnostic tracers, new therapeutic interventions, pre- and postcardiovascular event prognosis, and functional and pathophysiological heart conditions can be explored by microSPECT, using small-animal models of cardiovascular disease.

Dual molecular imaging for targeting metalloproteinase activity and apoptosis in atherosclerosis: molecular imaging facilitates understanding of pathogenesis.

BACKGROUND: Macrophage apoptosis and MMP activity contribute to vulnerability of atherosclerotic plaques to rupture. By employing molecular imaging techniques, we investigated if apoptosis and MMP release are interlinked. METHODS: Atherosclerosis was produced in rabbits receiving high-cholesterol diet (HC), who underwent dual radionuclide imaging with (99m)Tc-labeled matrix metalloproteinase inhibitor (MPI) and (111)In-labeled annexin A5 (AA5) using micro-SPECT/CT. %ID/g MPI and AA5 uptake was measured, followed by histological characterization. Unmanipulated animals were used as disease controls. Correlation between MPI and AA5 uptake was undertaken and relationship confirmed in culture study of activated THP-1 monocytes. RESULTS: MPI and AA5 uptake was best visualized in HC diet animals (n = 6) and reduced significantly after fluvastatin treatment (n = 4) or diet withdrawal (n = 3). %ID/g MPI (.087 +/- .018%) and AA5 (.03 +/- .01%) uptake was higher in HC than control (n = 6) animals (.014 +/- .004%, P < .0001; .0007 +/- .0002%, P < .0001), and reduced substantially after diet or statin intervention. There was a significant correlation between MPI and AA5 uptake (r = .62, P < .0001), both correlated with pathologically verified MMP-9 activity, macrophage content, and TUNEL staining. In vitro studies demonstrated MMP-9 release in culture medium from apoptotic THP-1 monocytes. CONCLUSIONS: The present study suggests that apoptosis and MMP are interrelated in atherosclerotic lesions and the targeting of more than one molecular candidate is feasible by molecular imaging.

Use of an oxygen-carrying blood substitute to improve intravascular optical coherence tomography imaging.

Optical coherence tomography (OCT) is a catheter-based imaging technology with powerful resolution capable of identifying vulnerable plaques and guiding coronary intervention. However, a significant limitation of intravascular OCT imaging is its attenuation by blood. We propose that the use of an oxygen-carrying blood substitute could potentially optimize OCT image quality. Surgical isolation of the descending thoracic aorta of six rabbits is performed, followed by intravascular OCT imaging of the abdominal aorta. Perfluorodecalin (PFD) is oxygenated using a bubble-through technique with 100% oxygen. OCT imaging is performed and compared using three different flushing modalities: PFD; saline; and blood. OCT imaging of the rabbit abdominal aorta is successful in all of the subjects. In each of the six studied subjects, flushing with PFD consistently provides dramatically better imaging of the vessel wall tissue structures. OCT image quality is highly dependent on the ability of the flushing modality to remove blood from the imaging field. From this proof-of-concept study, we demonstrate that endovascular flushing with an oxygen-carrying blood substitute (PFD) is optically superior to saline flushing for intravascular imaging.

Molecular imaging for efficacy of pharmacologic intervention in myocardial remodeling.

OBJECTIVES: Using molecular imaging techniques, we examined interstitial alterations during postmyocardial infarction (MI) remodeling and assessed the efficacy of antiangiotensin and antimineralocorticoid intervention, alone and in combination. BACKGROUND: The antagonists of the renin-angiotensin-aldosterone axis restrict myocardial fibrosis and cardiac remodeling after MI and contribute to improved survival. Radionuclide imaging with technetium-99m-labeled Cy5.5 RGD imaging peptide (CRIP) targets myofibroblasts and indirectly allows monitoring of the extent of collagen deposition post-MI. METHODS: CRIP was intravenously administered for gamma imaging after 4 weeks of MI in 63 Swiss-Webster mice and in 6 unmanipulated mice. Of 63 animals, 50 were treated with captopril (C), losartan (L), spironolactone (S) alone, or in combination (CL, SC, SL, and SCL), 8 mice received no treatment. Echocardiography was performed for assessment of cardiac remodeling. Hearts were characterized histopathologically for the presence of myofibroblasts and thick and thin collagen fiber deposition. RESULTS: Acute MI size was similar in all groups. The quantitative CRIP percent injected dose per gram uptake was greatest in the infarct area of untreated control mice (2.30 +/- 0.14%) and decreased significantly in animals treated with 1 agent (C, L, or S; 1.71 +/- 0.35%; p = 0.0002). The addition of 2 (CL, SC, or SL 1.31 +/- 0.40%; p < 0.0001) or 3 agents (SCL; 1.16 +/- 0.26%; p < 0.0001) demonstrated further reduction in tracer uptake. The decrease in echocardiographic left ventricular function, strain and rotation parameters, as well as histologically verified deposition of thin collagen fibers, was significantly reduced in treatment groups and correlated with CRIP uptake. CONCLUSIONS: Radiolabeled CRIP allows for the evaluation of the efficacy of neurohumoral antagonists after MI and reconfirms superiority of combination therapy. If proven clinically, molecular imaging of the myocardial healing process may help plan an optimal treatment for patients susceptible to heart failure.