Regional CZT myocardial perfusion reserve for the detection of territories with simultaneously impaired CFR and IMR in patients without obstructive coronary artery disease: a pilot study.

OBJECTIVES: To assess the diagnostic performances of CZT myocardial perfusion reserve (MPR) for the detection of territories with simultaneous impaired coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) in patients without obstructive coronary artery disease. METHODS: Patients were prospectively included before being referred for coronary angiography. All patients underwent CZT MPR before invasive coronary angiography (ICA) and coronary physiology assessment. Rest and dipyridamole-induced stress myocardial blood flow (MBF) and MPR were quantified using 99mTc-SestaMIBI and a CZT camera. Fractional flow reserve (FFR), Thermodilution CFR, and IMR were assessed during ICA. RESULTS: Between December 2016 and July 2019, 36 patients were included. 25/36 patients presented no obstructive coronary artery disease. A complete functional assessment was performed in 32 arteries. No territory presented a significant ischemia on CZT myocardial perfusion imaging. A moderate yet significant correlation was observed between regional CZT MPR and CFR (r = 0.4, P = .03). Sensitivity, specificity, positive and negative predictive value, and accuracy of regional CZT MPR versus the composite invasive criterion (impaired CFR and IMR) were 87 [47% to 99%], 92% [73% to 99%], 78% [47% to 93%], 96% [78% to 99%], and 91% [75% to 98%], respectively. All territories with a regional CZT MPR ≤ 1.8 showed a CFR < 2. Regional CZT MPR values were significantly higher in arteries with CFR ≥ 2 and IMR < 25 (negative composite criterion, n = 14) than in those with CFR < 2 and IMR ≥ 25 (2.6 [2.1 to 3.6] versus 1.6 [1.2 to 1.8]), P < .01). CONCLUSION: Regional CZT MPR presented excellent diagnostic performances for the detection of territories with simultaneously impaired CFR and IMR reflecting a very high cardiovascular risk in patients without obstructive coronary artery disease.

Noninvasive assessment of coronary microvascular dysfunction using SPECT myocardial perfusion imaging and myocardial perfusion entropy quantification in a rodent model of type 2 diabetes.

PURPOSE: Coronary microvascular dysfunction (CMVD) plays a major role in the occurrence of cardiovascular events (CVE). We recently suggested the clinical potential of myocardial perfusion entropy (MPE) quantification from SPECT myocardial perfusion images (MPI) for the prognosis of CVE occurrence. We hypothesized that the quantification of MPE from SPECT MPI would allow the assessment of CMVD-related MPE variations in a preclinical model of type 2 diabetes (T2D) including treatment with the anti-diabetic incretin liraglutide (LIR). METHODS: Optimal conditions for the preclinical quantification of MPE using 201Tl SPECT MPI were determined in rats with a T2D-like condition induced by a high-fat diet and streptozotocin injection (feasibility study, n = 43). Using such conditions, echocardiography and post-mortem LV capillary density evaluation were then used in order to assess the effect of LIR and the ability of MPE to assess CMVD (therapeutic study, n = 39). RESULTS: The feasibility study identified dobutamine stress and acute NO synthase and cyclooxygenase inhibition as optimal conditions for the quantification of MPE, with significant increases in MPE being observed in T2D animals (P < 0.01 vs controls). In the therapeutic study, T2D rats were hyperglycemic (5.5 ± 0.5 vs 1.1 ± 0.3 g/L for controls, P < 0.001) and had a significantly lower left ventricular ejection fraction (LVEF) (65 ± 4% vs 74 ± 9%, P < 0.01) and LV capillary density (2400 ± 300 vs 2800 ± 600 mm-3, P < 0.05). LIR partially restored glycemia (3.9 ± 0.6 g/L, P < 0.05 vs controls and T2D), totally prevented LVEF impairment (72 ± 7%, P = NS vs CTL), with no significant effect on capillary density. MPE was significantly increased in T2D rats (7.6 ± 0.5 vs 7.1 ± 0.5, P < 0.05), with no significant improvement in T2D-LIR rats (7.4 ± 0.4, P = NS vs controls and T2D). CONCLUSION: MPE quantification allowed the preclinical noninvasive assessment of CMVD. Both MPE and capillary density quantification suggested that LIR did not improve T2D-induced CMVD. The relevance of MPE for CMVD assessment warrants further clinical investigation.

Prognostic value of SPECT myocardial perfusion entropy in high-risk type 2 diabetic patients.

PURPOSE: Risk stratification of patients with type 2 diabetes mellitus (T2D) remains suboptimal. We hypothesized that myocardial perfusion entropy (MPE) quantified from SPECT myocardial perfusion images may provide incremental prognostic value in T2D patients independently from myocardial ischemia. METHODS: T2D patients with very high and high cardiovascular risk were prospectively included (n = 166, 65 ± 12 years). Stress perfusion defect was quantified by visual evaluation of SPECT MPI. SPECT MPI was also used for the quantification of rest and stress MPE. The primary end point was major adverse cardiac events (MACEs) defined as cardiac death, myocardial infarction (MI), and myocardial revascularization > 3 months after SPECT. RESULTS: Forty-four MACEs were observed during a 4.6-year median follow-up. Significant differences in stress MPE were observed between patients with and without MACEs (4.19 ± 0.46 vs. 3.93 ± 0.40; P ≤ .01). By Kaplan-Meier analysis, the risk of MACEs was significantly higher in patients with higher stress MPE (log-rank P ≤ 01). Stress MPE and stress perfusion defect (SSS ≥ 4) were significantly associated with the risk of MACEs (hazard ratio 2.77 and 2.06, respectively, P < .05 for both) after adjustment for clinical and imaging risk predictors as identified from preliminary univariate analysis. MPE demonstrated incremental prognostic value over clinical risk factors, stress test EKG and SSS as evidenced by nested models showing improved Akaike information criterion (AIC), reclassification (global continuous net reclassification improvement [NRI]: 63), global integrated discrimination improvement (IDI: 6%), and discrimination (change in c-statistic: 0.66 vs 0.74). CONCLUSIONS: Stress MPE provided independent and incremental prognostic information for the prediction of MACEs in diabetic patients. TRIAL REGISTRATION NUMBER: NCT02316054 (12/12/2014).

Prospective diagnostic performance of semiconductor SPECT myocardial perfusion imaging: wall thickening analysis reduces the need for an additional prone acquisition.

PURPOSE: To determine whether the assessment of regional wall thickening (WT) in addition to myocardial perfusion from stress supine acquisitions could compensate for the lack of prone acquisition and the corresponding decrease in the diagnostic performance of SPECT myocardial perfusion imaging (MPI) in patients with known or suspected coronary artery disease (CAD). METHODS: The study group comprised 41 patients (123 vessels) with known or suspected CAD prospectively recruited for systematic prone and supine 201Tl stress SPECT MPI. The diagnostic performance of SPECT MPI was determined for various image sets including nongated supine images (supine NG), nongated combined prone and supine images (prone and supine NG) and gated supine images, allowing WT evaluation from NG images in addition to perfusion (supine NG + WT) using invasive coronary angiography and fractional flow reserve as the gold standards. RESULTS: The rate of false positives was significantly higher among the supine NG images (20.8%) than among either the prone and supine NG or the supine NG + WT images (3.3% and 2.7%, respectively, P < 0.05 vs. supine NG). Consequently, specificity was higher for the prone and supine NG images than for the supine NG images (96.1% vs. 76.1%, P < 0.01) and was highest for the supine NG + WT images (96.8%, P not significant vs. prone and supine NG), without significant differences in sensitivity (80.0%, 86.6% and 73.3%, respectively, P not significant for all comparisons). CONCLUSION: The diagnostic performance of supine stress SPECT MPI is improved when WT assessment of ischaemic segments is used as an additional diagnostic criterion to values not significantly different from those with combined prone and supine acquisitions.

Sympathetic cardiac function in early sepsis: Noninvasive evaluation with [123I]-meta-iodobenzylguanidine (123I-MIBG) in vivo SPECT imaging.

BACKGROUND: Sympathetic system abnormalities have been reported in sepsis-related cardiac dysfunction. The present study aimed at evaluating the potential of the norepinephrine radiolabeled analogue [123I]-meta-iodobenzylguanidine (123I-MIBG) for the noninvasive assessment of modifications in cardiac sympathetic activity occurring in lipopolysaccharide (LPS)-induced experimental acute sepsis by single-photon emission computed tomographic imaging (SPECT). METHODS AND RESULTS: Sepsis was induced in male Wistar rats by intraperitoneal injection of 10 mg·kg-1 lipopolysaccharide (n = 16), whereas control animals (n = 7) were injected with vehicle (NaCl 0.9%). Echocardiography in LPS-injected animals (n = 8) demonstrated systolic and diastolic cardiac dysfunction. 123I-MIBG was injected 1 hour after LPS or vehicle administration (n = 8 and 7, respectively), and in vivo SPECT imaging was performed early and late (20 and 180 minutes) after tracer injection prior to animal euthanasia and ex vivo assessment of 123I-MIBG biodistribution. Global and 17-segment SPECT image analysis indicated that early 123I-MIBG activity was not affected by LPS treatment, whereas late cardiac tracer activity was significantly decreased in LPS-treated animals. Consequently, the cardiac washout of 123I-MIBG was significantly higher in LPS-treated (63.3% ± 4.0%) than that in control animals (56.7% ± 5.8%) (P < .05). CONCLUSION: Sepsis-induced modifications in cardiac sympathetic nervous system activity were evidenced by noninvasive in vivo 123I-MIBG SPECT imaging.

Nanobodies targeting mouse/human VCAM1 for the nuclear imaging of atherosclerotic lesions.

RATIONALE: A noninvasive tool allowing the detection of vulnerable atherosclerotic plaques is highly needed. By combining nanomolar affinities and fast blood clearance, nanobodies represent potential radiotracers for cardiovascular molecular imaging. Vascular cell adhesion molecule-1 (VCAM1) constitutes a relevant target for molecular imaging of atherosclerotic lesions. OBJECTIVE: We aimed to generate, radiolabel, and evaluate anti-VCAM1 nanobodies for noninvasive detection of atherosclerotic lesions. METHODS AND RESULTS: Ten anti-VCAM1 nanobodies were generated, radiolabeled with technetium-99m, and screened in vitro on mouse and human recombinant VCAM1 proteins and endothelial cells and in vivo in apolipoprotein E-deficient (ApoE(-/-)) mice. A nontargeting control nanobody was used in all experiments to demonstrate specificity. All nanobodies displayed nanomolar affinities for murine VCAM1. Flow cytometry analyses using human human umbilical vein endothelial cells indicated murine and human VCAM1 cross-reactivity for 6 of 10 nanobodies. The lead compound cAbVCAM1-5 was cross-reactive for human VCAM1 and exhibited high lesion-to-control (4.95±0.85), lesion-to-heart (8.30±1.11), and lesion-to-blood ratios (4.32±0.48) (P<0.05 versus control C57Bl/6J mice). Aortic arch atherosclerotic lesions of ApoE(-/-) mice were successfully identified by single-photon emission computed tomography imaging. (99m)Tc-cAbVCAM1-5 binding specificity was demonstrated by in vivo competition experiments. Autoradiography and immunohistochemistry further confirmed cAbVCAM1-5 uptake in VCAM1-positive lesions. CONCLUSIONS: The (99m)Tc-labeled, anti-VCAM1 nanobody cAbVCAM1-5 allowed noninvasive detection of VCAM1 expression and displayed mouse and human cross-reactivity. Therefore, this study demonstrates the potential of nanobodies as a new class of radiotracers for cardiovascular applications. The nanobody technology might evolve into an important research tool for targeted imaging of atherosclerotic lesions and has the potential for fast clinical translation.

Preclinical characterization of a novel radiolabeled analog of practolol for the molecular imaging of myocardial ß-adrenoceptor density.

BACKGROUND: The great clinical potential of myocardial ß-AR imaging has been shown by recent studies evaluating the ß-AR-specific, non-selective agent [(11)C]-CGP12177 in the setting of idiopathic-dilated cardiomyopathy, and myocardial infarction. However, the short half-life of (11)C hampers the potential of [(11)C]-CGP12177 for routine clinical use. AMI9 is an analog of the ß-adrenoceptor ligand practolol that can readily be labeled using radioactive isotopes of iodine. The present study was aimed at characterizing the in vitro, ex vivo, and in vivo ß-AR binding properties of [(125)I]-AMI9. METHODS AND RESULTS: Newborn rat cardiomyocytes were used for saturation and kinetic binding assays as well as for displacement and competition experiments. Isolated perfused rat hearts were used to evaluate the pharmacological activity of AMI9. The in vivo kinetics of [(125)I]-AMI9 were studied using biodistribution experiments in mice. [1(25)I]-AMI9 displayed high specific affinity for ß-AR with no ß-AR subtype selectivity (K D, 5.6 ± 0.3 nM; B max, 231 ± 7 fmol·(mg protein)(-1)). AMI9 potently inhibited the inotropic effects of isoproterenol. The early in vivo cardiac and lung activities of [(125)I]-AMI9 compared favorably with those of the clinically validated tracer CGP12177. CONCLUSION: Iodine-labeled AMI9 is a promising agent for the molecular imaging of myocardial ß-AR density.

Assessing low levels of mechanical stress in aortic atherosclerotic lesions from apolipoprotein E-/- mice--brief report.

OBJECTIVE: Despite the fact that mechanical stresses are well recognized as key determinants for atherosclerotic plaque rupture, very little is known about stress amplitude and distribution in atherosclerotic lesions, even in the standard apolipoprotein E (apoE)-/- mouse model of atherosclerosis. Our objectives were to combine immunohistology, atomic force microscopy measurements, and finite element computational analysis for the accurate quantification of stress amplitude and distribution in apoE-/- mouse aortic atherosclerotic lesions. METHODS AND RESULTS: Residual stresses and strains were released by radially cutting aortic arch segments from 7- to 30-week-old pathological apoE-/- (n=25) and healthy control mice (n=20). Immunohistology, atomic force microscopy, and biomechanical modeling taking into account regional residual stresses and strains were performed. Maximum stress values were observed in the normal arterial wall (276±71 kPa), whereas low values (<20 kPa) were observed in all plaque areas. Stress distribution was not correlated to macrophage infiltration. CONCLUSIONS: Low mechanical stress amplitude was observed in apoE-/- mouse aortic atherosclerotic lesions. This original study provides a basis for further investigations aimed at determining whether low stress levels are responsible for the apparently higher stability of murine aortic atherosclerotic lesions.

In vivo molecular imaging of myocardial angiogenesis using the alpha(v)beta3 integrin-targeted tracer 99mTc-RAFT-RGD.

BACKGROUND: Myocardial angiogenesis following reperfusion of an infarcted area may impact on patient prognosis and pro-angiogenic treatments are currently evaluated. The non-invasive imaging of angiogenesis would therefore be of potential clinical relevance in these settings. (99m)Tc-RAFT-RGD is a novel (99m)Tc-labeled tracer that targets the alpha(v)beta(3) integrin. Our objective was to determine whether this tracer was suitable for myocardial angiogenesis imaging. METHODS AND RESULTS: A rat model of reperfused myocardial infarction was employed. Fourteen days following reperfusion, the animals were injected with (99m)Tc-RAFT-RGD or with its negative control (99m)Tc-RAFT-RAD. Fourteen animals were dedicated to autoradiographic imaging, infarct staining, and gamma-well counting of myocardial activity. In vivo dual-isotope pinhole SPECT imaging of (201)Tl and (99m)Tc-RAFT-RGD or (99m)Tc-RAFT-RAD was also performed in 11 additional animals. Neovessels were observed by immunostaining in the infarcted and peri-infarct areas. (99m)Tc-RAFT-RGD infarct-to-normal ratios by gamma-well counting and ex vivo imaging (2.5 +/- 0.6 and 4.9 +/- 0.9, respectively) were significantly higher than those of (99m)Tc-RAFT-RAD (1.7 +/- 0.2 and 2.2 +/- 0.4, respectively, P < .05). The infarcted area was readily visible in vivo by SPECT with (99m)Tc-RAFT-RGD but not with (99m)Tc-RAFT-RAD (infarct-to-normal zone activity ratio, 2.5 +/- 0.6 and 1.7 +/- 0.4, respectively, P < .05). CONCLUSION: (99m)Tc-RAFT-RGD allowed the experimental in vivo molecular imaging of myocardial angiogenesis.

Evaluation of Antiatherogenic Properties of Ezetimibe Using 3H-Labeled Low-Density-Lipoprotein Cholesterol and 99mTc-cAbVCAM1-5 SPECT in ApoE-/- Mice Fed the Paigen Diet.

The addition of ezetimibe, an intestinal cholesterol absorption inhibitor, to statin therapy has recently shown clinical benefits in the Improved Reduction of Outcomes: Vytorin Efficacy International Trial by reducing low-density-lipoprotein (LDL) cholesterol levels more than statin therapy alone. Here, we investigated the mechanisms by which inhibition of intestinal cholesterol absorption might contribute to the clinically observed reduction in cardiovascular events by evaluating its effect on inflammatory plaque development in apolipoprotein E-/- mice. Methods: Apolipoprotein E-/- mice were fed the Paigen diet (1.25% cholesterol, 0.5% cholic acid, and 15% fat) without or with ezetimibe (7 mg/kg/d) for 6 wk. In a first set of mice (n = 15), we intravenously injected 3H-cholesteryl oleate-labeled human LDL to test whether ezetimibe promotes LDL-derived cholesterol fecal excretion. In a second set (n = 20), we used the imaging agent 99mTc-cAbVCAM1-5 to evaluate expression of an inflammatory marker, vascular cell adhesion molecule 1 (VCAM-1), in atherosclerotic plaques. In a third set (n = 21), we compared VCAM-1 expression with 99mTc-cAbVCAM1-5 uptake in various tissues. Results: Mice treated with ezetimibe showed a 173% higher LDL-cholesteryl ester plasma disappearance rate (P < 0.001 vs. control) after 3H-cholesteryl oleate-labeled LDL injection. At 96 h after injection, the hepatic fraction of 3H-tracer was 61% lower in mice treated with ezetimibe (P < 0.001). Meanwhile, LDL-derived 3H-cholesterol excretion in the feces was 107% higher (P < 0.001). The antiatherogenic effect of ezetimibe monitored by 99mTc-cAbVCAM1-5 SPECT showed a 49% reduction in aortic tracer uptake (percentage injected dose per cubic centimeter, 0.95 ± 0.04 vs. 1.87 ± 0.11; P < 0.01). In addition to hypercholesterolemia, the proinflammatory Paigen diet significantly increased VCAM-1 expression with respect to the control group in various tissues, including the aorta, and this expression correlated strongly with 99mTc-cAbVCAM1-5 uptake (r = 0.75; P < 0.05). Conclusion: Inhibition of intestinal cholesterol absorption with ezetimibe promotes antiatherosclerotic effects through increased LDL cholesterol catabolism and LDL-derived cholesterol fecal excretion and reduces inflamed atherosclerotic plaques. These mechanisms may contribute to the benefits of adding ezetimibe to a statin therapy.

Organ biodistribution and myocardial uptake, washout, and redistribution kinetics of Tc-99m N-DBODC5 when injected during vasodilator stress in canine models of coronary stenoses.

BACKGROUND: Technetium 99m N-DBODC5 is a new myocardial perfusion tracer shown to exhibit high heart uptake and rapid liver clearance in normal rats. The objectives of this canine study were (1) to compare the organ biodistribution and myocardial uptake, washout, and redistribution kinetics of Tc-99m N-DBODC5 with Tc-99m sestamibi over a period of 3 hours in a more clinically relevant large animal species and (2) to compare the myocardial uptake of Tc-99m N-DBODC5 with thallium 201 when co-injected during vasodilator stress in dogs with coronary stenoses. METHODS AND RESULTS: At peak adenosine-induced hyperemia, 10 dogs with critical left anterior descending artery stenoses received either Tc-99m N-DBODC5 (n = 6) or Tc-99m sestamibi (n = 4) and microspheres, followed by serial imaging and blood sampling over a period of 3 hours. Another 14 dogs with either critical (n = 7) or mild (n = 7) left anterior descending artery stenoses underwent simultaneous injection of Tc-99m N-DBODC5, Tl-201, and microspheres during peak vasodilator stress. Like sestamibi, Tc-99m N-DBODC5 showed good myocardial uptake with slow washout and minimal redistribution over a period of 3 hours (P = not significant); however, Tc-99m N-DBODC5 cleared more rapidly from the liver (heart-lung ratio at 30 minutes, 0.92+/-0.11 versus 0.51 +/- 0.05; P < .05). When injected during hyperemic flow, the myocardial extraction plateau for Tc-99m N-DBODC5 was lower than that for Tl-201 and was intermediate between Tc-99m sestamibi and Tc-99m tetrofosmin. CONCLUSIONS: Excellent organ biodistribution and myocardial uptake and clearance kinetic properties, combined with rapid liver clearance and a favorable flow-extraction relationship, make Tc-99m N-DBODC5 a very promising new myocardial perfusion imaging agent.

Assessment of myocardial inflammation produced by experimental coronary occlusion and reperfusion with 99mTc-RP517, a new leukotriene B4 receptor antagonist that preferentially labels neutrophils in vivo.

BACKGROUND: 99mTc-RP517 is a new leukotriene B4 (LTB4) receptor antagonist developed for imaging acute inflammation or infection. A unique property of 99mTc-RP517 is its ability to label white blood cells in vivo after intravenous injection. The goals of this study were to determine relative 99mTc-RP517 binding to human leukocyte subtypes and the 99mTc-RP517 uptake pattern in canine myocardium where inflammation was induced by either coronary occlusion and reperfusion or tumor necrosis factor alpha (TNFalpha) injection. METHODS AND RESULTS: Fluorescence-activated cell sorter analysis was performed on whole human blood (n=2) and isolated neutrophils (n= 4) with a fluorescent analog of 99mTc-RP517, [F]-RP517. In whole blood, [F]-RP517 (500 nmol/L) preferentially labeled neutrophils. On isolated neutrophils, [F]-RP517 (10 nmol/L) binding was inhibited by 44% when LTB4 (400 nmol/L) was added. 99mTc-RP517 was injected intravenously in anesthetized, open-chest dogs before coronary occlusion (90 minutes) and reperfusion (120 minutes) (n=9) or before intramyocardial TNFalpha injection (n=3). Ex vivo images of heart slices were acquired. The left ventricle was divided into 72 segments for flow and 99mTc-RP517 uptake analysis. There was an inverse exponential relationship between 99mTc-RP517 uptake and occlusion flow (r=0.73). In the same 15 segments, 99mTc-RP517 uptake was highly correlated with the neutrophil enzyme myeloperoxidase (r=0.91). Ex vivo images revealed tracer uptake in the reperfused area (ischemic to normal count ratio=2.7+/-0.2). CONCLUSIONS: RP517 binds to the neutrophil LTB4 receptor after intravenous injection. After reperfusion, 99mTc-RP517 uptake correlated with myeloperoxidase and was observed on ex vivo images, indicating that this tracer may have potential as an inflammation-imaging agent.

Influence of propranolol, enalaprilat, verapamil, and caffeine on adenosine A(2A)-receptor-mediated coronary vasodilation.

OBJECTIVES: The study was done to determine the effects of propranolol, enalaprilat, verapamil, and caffeine on the vasodilatory properties of the adenosine A(2A)-receptor agonist ATL-146e (ATL). BACKGROUND: ATL is a new adenosine A(2A)-receptor agonist proposed as a vasodilator for myocardial stress perfusion imaging. Beta-blockers, angiotensin-converting enzyme (ACE) inhibitors, and calcium blockers are commonly used for the treatment of coronary artery disease (CAD), and their effect on ATL-mediated vasodilation is unknown. Dietary intake of caffeine is also common. METHODS: In 19 anesthetized, open-chest dogs, hemodynamic responses to bolus injections of ATL (1.0 microg/kg) and adenosine (60 microg/kg) were recorded before and after administration of propranolol (1.0 mg/kg, ATL only), enalaprilat (0.3 mg/kg, ATL only), caffeine (5.0 mg/kg, ATL only), and verapamil (0.2 mg/kg bolus, ATL and adenosine). RESULTS: Neither propranolol nor enalaprilat attenuated the ATL-mediated vasodilation (225 +/- 86% and 237 +/- 67% increase, respectively, p = NS vs. control). Caffeine had an inhibitory effect (97 +/- 28% increase, p < 0.05 vs. control). Verapamil blunted both ATL- and adenosine-induced vasodilation (63 +/- 20% and 35 +/- 7%, respectively, p < 0.05 vs. baseline), and also inhibited the vasodilation induced by the adenosine triphosphate-sensitive potassium (K(ATP)) channel activator pinacidil. CONCLUSIONS: Beta-blockers and ACE inhibitors do not reduce the maximal coronary flow response to adenosine A(2A)-agonists, whereas verapamil attenuated this vasodilation through inhibition of K(ATP) channels. The inhibitory effect of verapamil and K(ATP) channel inhibitors like glybenclamide on pharmacologic stress using adenosine or adenosine A(2A)-receptor agonists should be evaluated in the clinical setting to determine their potential for reducing the sensitivity of CAD detection with perfusion imaging.

Effects of increased lipid concentration and hyperemic blood flow on the intrinsic myocardial washout kinetics of (99m)TcN-NOET.

UNLABELLED: Bis(N-ethoxy,N-ethyldithiocarbamato)nitrido technetium (V) ((99m)Tc) ((99m)TcN-NOET) is a myocardial perfusion imaging agent demonstrating significant redistribution and currently in phase III clinical trials. Previous studies have suggested that (99m)TcN-NOET is bound intravascularly. Therefore, we sought to determine whether modifications in the vascular compartment would provide further insights into the mechanisms of (99m)TcN-NOET myocardial washout and redistribution. METHODS: (99m)TcN-NOET cardiac washout was studied ex vivo in 15 isolated perfused rat hearts after bolus injection (1.5 MBq) in the absence (n = 6) or presence of bovine serum albumin ([BSA] 0.03%) with (n = 5) or without (n = 4) bound lipids. The intrinsic myocardial washout of the tracer was also studied in vivo in 6 dogs after intracoronary bolus injection of the tracer (0.75 MBq) before and after hyperlipidemia induced by intravenous administration of 300 mL of 20% intralipids (n = 3) or hyperemia induced by intravenous infusion of the adenosine A(2A) receptor agonist ATL-146e (0.3 micro g/kg/min; n = 6). RESULTS: On isolated hearts, there was no significant myocardial washout of (99m)TcN-NOET with Krebs-Henseleit buffer. Addition of BSA without bound lipids resulted in a significant cardiac washout of the tracer (P < 0.001 by repeated measures ANOVA). The presence of lipids bound to BSA further accelerated the washout rate of (99m)TcN-NOET (half-life [t(1/2)], 431.5 +/- 23.2 min vs. 242.9 +/- 63.2 min; P < 0.05). In vivo in dogs, intralipid administration significantly increased the intrinsic washout rate of (99m)TcN-NOET (t(1/2), 108.0 +/- 23.9 min vs. 51.8 +/- 11.8 min; P < 0.05). In addition, vasodilatation with ATL-146e resulted in a 4.9-fold increase in coronary flow (P < 0.05 vs. baseline) and a significantly faster intrinsic (99m)TcN-NOET myocardial washout (t(1/2), 81.1 +/- 12.1 min vs. 40.7 +/- 7.3 min; P < 0.05). CONCLUSION: The myocardial washout kinetics of (99m)TcN-NOET are affected by a variety of intravascular factors, supporting the hypothesis that the tracer is most likely localized on the vascular endothelium. The potential impact of variations in circulating lipid levels among patients on clinical imaging with (99m)TcN-NOET requires further investigation.

Verapamil does not inhibit 99mTcN-NOET uptake in situ in normal or ischemic canine myocardium.

UNLABELLED: Bis(N-ethoxy,N-ethyldithiocarbamato)nitrido technetium (V) ((99m)Tc) ((99m)TcN-NOET) is a new myocardial perfusion imaging agent currently undergoing phase III clinical trials in the United States and in Europe. (99m)TcN-NOET cellular uptake has been shown to be inhibited by the calcium channel inhibitor verapamil in cultured newborn rat cardiomyocytes. However, the effect of verapamil on in situ (99m)TcN-NOET myocardial uptake remains unknown. Therefore, the aim of this study was to evaluate whether the inhibitory effect of verapamil on the cellular uptake of (99m)TcN-NOET shown in vitro could be reproduced in situ in a canine model of normal and ischemic myocardium. METHODS: (99m)TcN-NOET uptake in normal and ischemic myocardium (70% flow reduction in the left anterior descending coronary artery) was measured in the absence or presence of verapamil (0.015 mg/kg/min x 10 min) in anesthetized, open-chest dogs (n = 17). Control animals were infused with adenosine (0.2 mg/kg/min) to match the verapamil-induced increase in flow. RESULTS: By verapamil treatment, a clinically relevant plasma concentration of the calcium channel inhibitor was attained (mean +/- SEM, 290 +/- 152 ng/mL). In normal myocardium (n = 8), regional blood flow at the time of (99m)TcN-NOET injection was not statistically different in verapamil- and adenosine-treated dogs (1.69 +/- 0.03 vs. 1.61 +/- 0.04 mL/min/g, respectively). (99m)TcN-NOET uptake was slightly higher in the presence of verapamil (0.39 +/- 0.01 vs. 0.38 +/- 0.01 counts per minute [cpm]/[Bq/kg]/g for adenosine; P = 0.04). However, no significant difference in (99m)TcN-NOET myocardial uptake was observed after normalization of the tracer uptake to regional myocardial blood flow. In ischemic myocardium (n = 9), regional blood flow was lower in verapamil-treated than in adenosine-treated animals (0.22 +/- 0.02 vs. 0.29 +/- 0.03 mL/min/g; P < 0.05). (99m)TcN-NOET uptake in the ischemic area was not inhibited by verapamil (0.09 +/- 0.01 vs. 0.10 +/- 0.01 cpm/[Bq/kg]/g; P = not significant). CONCLUSION: Verapamil does not inhibit (99m)TcN-NOET uptake in situ in normal and ischemic canine myocardium. These results suggest that verapamil should not affect (99m)TcN-NOET myocardial uptake in patients referred for myocardial perfusion imaging.

99mTc-N-DBODC5, a new myocardial perfusion imaging agent with rapid liver clearance: comparison with 99mTc-sestamibi and 99mTc-tetrofosmin in rats.

UNLABELLED: (99m)Tc-[bis (dimethoxypropylphosphinoethyl)-ethoxyethylamine (PNP5)]-[bis (N-ethoxyethyl)-dithiocarbamato (DBODC)] nitride (N-PNP5-DBODC or N-DBODC5) is a new monocationic myocardial perfusion tracer. We sought to compare the myocardial uptake and clearance kinetics and organ biodistribution of (99m)Tc-N-DBODC5 with (99m)Tc-sestamibi and (99m)Tc-tetrofosmin. METHODS: Seventy-five anesthetized Sprague-Dawley rats were injected intravenously with 22.2-29.6 MBq (99m)Tc-N-DBODC5 (n = 25), (99m)Tc-sestamibi (n = 25), or (99m)Tc-tetrofosmin (n = 25). Rats were euthanized at either 2, 10, 20, 30, or 60 min after injection and gamma-well counting was performed on excised organ (heart, lung, and liver) and blood samples. In 3 additional rats, serial in vivo whole-body gamma-camera imaging with each tracer was performed. RESULTS: (99m)Tc-N-DBODC5 cleared rapidly from the blood pool. At 2 min after injection, (99m)Tc-N-DBODC5 blood activity was significantly lower than either (99m)Tc-sestamibi or (99m)Tc-tetrofosmin (P < 0.01) and remained lower over 60 min. Myocardial (99m)Tc-N-DBODC5 uptake was rapid (2.9% +/- 0.1% injected dose/g at 2 min), and there was no significant clearance over 60 min, similar to (99m)Tc-sestamibi and (99m)Tc-tetrofosmin. All 3 tracers exhibited rapid lung clearance. Importantly, (99m)Tc-N-DBODC5 cleared more rapidly from the liver than either (99m)Tc-sestamibi or (99m)Tc-tetrofosmin. As early as 30 min after injection, (99m)Tc-N-DBODC5 heart-to-liver ratio was 5.7 +/- 1.0 versus 1.6 +/- 0.1 and 2.9 +/- 0.3 for (99m)Tc-sestamibi and (99m)Tc-tetrofosmin (P < 0.05). By 60 min, (99m)Tc-N-DBODC5 heart-to-liver ratio further increased to 18.4 +/- 2.0 compared with 2.6 +/- 0.2 and 5.8 +/- 0.7 for (99m)Tc-sestamibi and (99m)Tc-tetrofosmin (P < 0.001). The rapid blood pool, lung, and liver clearance of (99m)Tc-N-DBODC5 resulted in excellent-quality myocardial images within 30 min after injection. CONCLUSION: (99m)Tc-N-DBODC5 is a promising new myocardial perfusion tracer with superior biodistribution properties. The rapid (99m)Tc-N-DBODC5 liver clearance may shorten the duration of imaging protocols by allowing earlier image acquisition and may markedly reduce the problem of photon scatter from the liver into the inferoapical wall on myocardial images.

Periaortic brown adipose tissue as a major determinant of [¹8F]-fluorodeoxyglucose vascular uptake in atherosclerosis-prone, apoE-/- mice.

BACKGROUND: [18F]-fluorodeoxyglucose (FDG) has been suggested for the clinical and experimental imaging of inflammatory atherosclerotic lesions. Significant FDG uptake in brown adipose tissue (BAT) has been observed both in humans and mice. The objective of the present study was to investigate the influence of periaortic BAT on apolipoprotein E-deficient (apoE-/-) mouse atherosclerotic lesion imaging with FDG. METHODS: ApoE-/- mice (36 ± 2 weeks-old) were injected with FDG (12 ± 2 MBq). Control animals (Group A, n = 7) were injected conscious and kept awake at room temperature (24°C) throughout the accumulation period. In order to minimize tracer activity in periaortic BAT, Group B (n = 7) and C (n = 6) animals were injected under anaesthesia at 37°C and Group C animals were additionally pre-treated with propranolol. PET/CT acquisitions were performed prior to animal euthanasia and ex vivo analysis of FDG biodistribution. RESULTS: Autoradiographic imaging indicated higher FDG uptake in atherosclerotic lesions than in the normal aortic wall (all groups, P<0.05) and the blood (all groups, P<0.01) which correlated with macrophage infiltration (R = 0.47; P<0.001). However, periaortic BAT uptake was either significantly higher (Group A, P<0.05) or similar (Group B and C, P = NS) to that observed in atherosclerotic lesions and was shown to correlate with in vivo quantified aortic FDG activity. CONCLUSION: Periaortic BAT FDG uptake was identified as a confounding factor while using FDG for the non-invasive imaging of mouse atherosclerotic lesions.

Effects of mechanical properties and atherosclerotic artery size on biomechanical plaque disruption - mouse vs. human.

Mouse models of atherosclerosis are extensively being used to study the mechanisms of atherosclerotic plaque development and the results are frequently extrapolated to humans. However, major differences have been described between murine and human atherosclerotic lesions and the determination of similarities and differences between these species has been largely addressed recently. This study takes over and extends previous studies performed by our group and related to the biomechanical characterization of both mouse and human atherosclerotic lesions. Its main objective was to determine the distribution and amplitude of mechanical stresses including peak cap stress (PCS) in aortic vessels from atherosclerotic apoE(-/-) mice, in order to evaluate whether such biomechanical data would be in accordance with the previously suggested lack of plaque rupture in this model. Successful finite element analysis was performed from the zero-stress configuration of aortic arch sections and mainly indicated (1) the modest role of atherosclerotic lesions in the observed increase in residual parietal stresses in apoE(-/-) mouse vessels and (2) the low amplitude of murine PCS as compared to humans. Overall, the results from the present study support the hypothesis that murine biomechanical properties and artery size confer less propensity to rupture for mouse lesions in comparison with those of humans.