15th European Molecular Imaging Meeting
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Heart Diseases

Session chair: Janette Iking (Essen, Germany); Pierre Sicard (Paris, France)
 
Shortcut: PW21
Date: Friday, 28 August, 2020, 12:00 p.m. - 1:30 p.m.
Session type: Poster

Contents

Abstract/Video opens by clicking at the talk title.

315

Macrophage depletion impairs cardiac repair after acute myocardial infarction: Insights from multimodality molecular imaging in mice

Annika Hess1, Laura B. N. Langer1, Tobias L. Ross1, Hans-Jürgen Wester2, Frank M. Bengel1, James T. Thackeray1

1 Hannover Medical School, Department of Nuclear Medicine, Hannover, Germany
2 Technical University of Munich, Chair of Radiopharmaceutical Chemistry, Garching, Germany

Introduction

Cardiac repair after acute myocardial infarction (MI) involves a dynamic inflammatory response. Macrophages participate in both clearance of debris and remodelling. While modulating infiltrating leukocytes may improve outcomes, complete inflammatory suppression may be detrimental. We investigated the effects of peripheral macrophage depletion on early myocardial inflammation and subsequent functional outcome after acute MI in mice using cardiac magnetic resonance (CMR) and PET imaging of chemokine receptor CXCR4.

Methods

C57Bl6 mice received clodronate-loaded liposomes for peripheral macrophage depletion (n=12) or PBS-loaded liposomes as vehicle control (n=6). After 24h, mice underwent permanent left coronary artery ligation (MI) or sham surgery. Inflammation was assessed on MI+1d, 3d, and 7d by CXCR4-targeted PET/CT using 68Ga-pentixafor. Perfusion 99mTc-sestamibi SPECT/CT calculated infarct sizes and CMR assessed left ventricular (LV) function at MI+1wk and 6wks. Microcalcification was tested by 18F-NaF PET/CT at MI+4wks. Immunohistochemistry characterized cellular basis of inflammatory imaging signal.

Results/Discussion

PET revealed increased infarct CXCR4 expression after macrophage depletion compared to vehicle over 7d post-MI (%injected dose (ID)/g; d1: 1.6±0.2 vs 1.2±0.1; d3: 1.3±0.2 vs 1.0±0.2; d7: 1.1±0.4 vs 0.7±0.1; p<0.05). Histology confirmed macrophage depletion, but elevated recruitment of neutrophils in the infarct. Over 7d post-MI, macrophage depletion increased LV rupture rate compared to vehicle (42% vs 16%). Surviving mice showed LV dilatation (end systolic volume (µl), 97±50 vs 98±55, p=0.98) accompanied by impaired LV ejection fraction (%, 32±8 vs 29±10, p=0.61). Similar infarct size was found for both groups (%LV, clodronate: 38±8 vs vehicle 32±8, p=0.3). CMR revealed a dense intra-cavity thrombus adherent to the infarct wall at 7d post-MI. 18F-NaF PET/CT identified active calcification in the intraluminal thrombus at 4wks, which was absent in vehicle-treated MI and macrophage-depleted sham. Scar region calcification was confirmed by CT in macrophage-depleted mice at MI+6wks.

Conclusions

Absence of peripheral macrophages alters the inflammatory pattern post-MI including higher neutrophil recruitment, increased LV rupture rate, thrombus formation and tissue calcification. This underscores the necessity of macrophages for effective healing, and may explain adverse response to broad anti-inflammatory therapy in myocardial ischemia.

Macrophage depletion impaires wound healing after myocardial infarction
A) Cardiac short axis PET images demonstrate higher CXCR4 expression (color scale) after macrophage depletion by clodronate within the 18F-FDG defined infarct (grey scale) compared to vehicle at MI+3d. B) Macrophage depletion leads to left ventricular thrombus formation (red arrow) as visualized by CMR which is absent in vehicle-treated mice at MI+1wk. C) 18F-NaF PET images in a mouse after macrophage depletion show active calcification in the infarct at MI+4wks co-localized to calcified area determined by CT whereas no cardiac NaF or CT signal is observed in vehicle-treated mice.
Keywords: Inflammation imaging, PET, CMR, Macrophages
316

The novel TSPO radiotracer, [18F]LW223, identifies cardiac inflammation in a rat myocardial infarction model

Mark G. MacAskill1, 2, Agne Stadulyte1, 2, Lewis Williams3, Timaeus E. F. Morgan1, 2, Nikki L. Sloan3, Carlos J. Alcaide-Corral1, 2, Tashfeen Walton1, 2, Nick Spath1, William Mungall4, Marc R. Dweck1, Gillian A. Gray1, David E. Newby1, Christophe Lucatelli2, Andrew Sutherland3, Sally L. Pimlott5, 6, Adriana A. S. Tavares1, 2

1 University of Edinburgh, University/BHF Centre for Cardiovascular Science, Edinburgh, United Kingdom
2 University of Edinburgh, Edinburgh Imaging, Edinburgh, United Kingdom
3 University of Glasgow, WestCHEM, Glasgow, United Kingdom
4 University of Edinburgh, Bioresearch and Veterinary Services, Edinburgh, United Kingdom
5 University of Glasgow, School of Medicine, Glasgow, United Kingdom
6 NHS Greater Glasgow and Clyde, Glasgow, United Kingdom

Introduction

For several decades, the 18kDa Translocator protein (TSPO) has been a molecular imaging target for inflammation. Evidence has emerged indicating that myocardial infarction (MI) can lead to subsequent neuroinflammation, all of which can be detected by targeting TSPO1. We have developed a novel TSPO ligand, LW223, which has binding independent of the rs6971 polymorphism and good in vivo characteristics. This study aims to assess the ability of [18F]LW223 to detect macrophage driven inflammation in the rat permanent coronary artery ligation model.

Methods

Adult male Sprague-Dawley rats underwent permanent ligation of the left anterior descending artery to induce MI. On day 3 post-MI, infarcts were assessed by ultrasound and on day 7 PET/CT imaging with [18F]LW223 was performed. Naive male Sprague-Dawley rats were used as a healthy control comparison. Perfusion-corrected PET data was generated using two-tissue compartmental modelling with K1 (rate constant for transfer from arterial plasma to tissue) acting as a surrogate perfusion marker to correct the Binding Potential for impaired radiotracer transfer from arterial plasma to tissue and derive a new constant BPTC.

Results/Discussion

Ultrasound at day 3 post-MI confirm the presence of considerable anterior wall infarcts. Quantification of BPTC from day 7 PET data demonstrated a significant increase in [18F]LW223 binding within the infarct of the MI group relative to a similar region in the healthy controls (Fig. 1A & B, 36.9± 8.8 vs. 10.0± 2.4 cm3/ml/min, p≤0.001). The PET data was validated using ex-vivo immunofluorescent staining for CD68 (macrophage marker) and TSPO, which resulted in the same pattern of signal as in vivo PET (Fig. 1C & D respectively). This ex-vivo analysis demonstrated that the new constant BPTC is able to quantify disease activity better than traditional distribution volumes (VT). [18F]LW223 binding in the brain did not change between healthy and MI subjects; however a strong correlation between the level of BPTC in the heart and brain was evident.

Conclusions

[18F]LW223 can be used to image and quantify macrophage-driven inflammation in the heart following myocardial infarction. Further studies are now underway to investigate this approach at different time points, and in the more clinically relevant reperfusion model.

AcknowledgmentThe authors would like to thank the British Heart Foundation for funding this work (PG/17/83/33370).
References
[1] Thackeray JT et al. J.Am.Col.Cardiol 2018;71:263–275.
[18F]LW223 PET/CT in a rat model of myocardial infarction
Keywords: Myocardial Infarction, TSPO, Inflammation, Macrophage, PET
318

Characterization of Takotsubo-like animal model by concurrent molecular and functional in vivo Imaging

Thulaciga Yoganathan1, Mailyn Perez-Liva1, 2, Anais Certain1, Gilles Renault4, Franck Lager4, Clement Papadacci3, Alicia Arévalo Garcia1, Mickael Tanter3, Thomas Viel1, 2, Bertrand Tavitian1, 2

1 Université de Paris, Inserm UMR970, Paris, France
2 Plateforme d’Imageries du Vivant, Paris Cardiovascular Research Center, Paris, France
3 Physics for Medicine Paris, Inserm U1273, ESPCI Paris, CNRS, PSL University, Paris, France
4 Plateforme d’Imageries du Vivant, Institut Cochin, INSERM U1016, Paris, France

Introduction

The Takotsubo syndrome (TTS), affecting mainly post-menopause women, is a transient left ventricular apical ballooning induced by emotional or physical stress. Clinically, TTS signs are similar to acute coronary syndromes (ACS), but there is no coronary obstruction and the regional wall motion abnormalities are reversible1-2. Although TTS signs revert without treatment, long term mortality of TTS is similar to that of ACS3 and its pathophysiology is poorly understood. Here we present the results of a longitudinal concurrent functional and molecular imaging study of a rodent TTS model in rats.

Methods

TTS was induced in 9 female Wistar rats by intraperitoneal injection of isoprenaline (ISO, 50 mg/kg, experimentation authorization n°19-064). PETRUS imaging7 for simultaneous PET, CT and Ultrafast Ultrasound Imaging (UUI)), was repeated 3 times in each animal, before, 2h and 7 days after ISO. Heart rate, ECG and respiration were monitored. PET data was acquired during 60 min after IV injection of [18F]FDG (37±0.8 MBq). Simultaneously, UUI images of the heart were obtained using a 12 MHz probe. PET and UUI were co-registered as previously described8. PET scans were reconstructed using customized 3D-OSEM and quantified using PMOD. Brain Natriuretic Peptide (BNP) was measured in blood samples. Rats were euthanatized at day 7, hearts were stained with Sirius Red to assess myocardial fibrosis.

Results/Discussion

Heart rate increased 2h post ISO (p =<0.0001, 38% of difference) and returned to baseline values at day 7 as well as the respiratory rate (p<0.0001, 40% of difference). ECG showed ST-segment prolongations and S wave elevations at 2h, indicating impaired LV repolarization and contraction. US imaging showed systolic dysfunction at 2h that had fully recovered at day 7 (cf. fig.(A)). PET imaging showed a basal and apical metabolic remodeling at day 7 (mean SUV= 11.1 ± 3.3 vs. 8.7 ± 2.3 at baseline and 7.9 ± 2.30 at 2h) (cf. fig.(B)). There is increased fibrosis in the apex of the LV at day 7 compared to healthy animals and basal region of LV (p=0.0017) (cf. fig.(C)). Plasmatic BNP concentration increased at day 7 compared to control and 2h. In summary, in spite of the recovery of LV function and morphology at day 7 compared to 2h, PET imaging showed metabolic regional remodeling at 7 days post ISO, which was confirmed by histology and BNP plasmatic dosage.

Conclusions

The ISO rat model presents signs similar to the clinical descriptions: ECG abnormalities, high heart rate and LV function’s reversibility1-2. Interestingly, while at day 7 the LV function had been restored, PET evidenced an important metabolic remodeling, coinciding with LV fibrosis. Our results suggest that metabolic changes observed using FDG PET imaging could be a useful imaging biomarker to assess the evolution of TTS syndrome.

Acknowledgment

In vivo imaging was performed at the Life Imaging Facility of Paris Descartes University (Plateforme Imageries du Vivant - PIV), supported by France Life Imaging (grant ANR-11-INBS-0006) and Infrastructures Biologie-Santé (IBISA).

References
[1] Templin, C., Ghadri, J. R., Diekmann, J., Napp, L. C., Bataiosu, D. R., Jaguszewski, M., ... & Seifert, B. (2015). Clinical features and outcomes of Takotsubo (stress) cardiomyopathy. New England Journal of Medicine, 373(10), 929-938.
[2] Ghadri, J. R., Wittstein, I. S., Prasad, A., Sharkey, S., Dote, K., Akashi, Y. J., ... & Yoshida, T. (2018). International expert consensus document on Takotsubo syndrome (part I): clinical characteristics, diagnostic criteria, and pathophysiology. European heart journal, 39(22), 2032-2046.
[3] Ghadri, J. R., Kato, K., Cammann, V. L., Gili, S., Jurisic, S., Di Vece, D., ... & Bacchi, B. (2018). Long-term prognosis of patients with Takotsubo syndrome. Journal of the American College of Cardiology, 72(8), 874-882.
[4] Provost, J., Garofalakis, A., Sourdon, J., Bouda, D., Berthon, B., Viel, T., ... & Pernot, M. (2018). Simultaneous positron emission tomography and ultrafast ultrasound for hybrid molecular, anatomical and functional imaging. Nature biomedical engineering, 2(2), 85.
[5] Perez-Liva, M., Viel, T., Yoganathan, T., Garofalakis, A., Sourdon, J., Facchin, C., ... & Tavitian, B. (2018). Performance evaluation of the PET component of a hybrid PET/CT-ultrafast ultrasound imaging instrument. Physics in Medicine & Biology, 63(19), 19NT01.
Myocardial functional and molecular remodeling in Takotsubo-like animal model.

Although there was a recovery of LV function and morphology at day 7 post ISO compared to 2h (A), FDG PET imaging showed a metabolic remodeling at 7 days post ISO (B), which coincided with an increase of myocardial fibrosis (p=0.0008, non-parametric Mann-Whitney test) (C).

Keywords: Takotsubo syndrome, Acute Cardiomyopathy Induced by Stress, FDG PET, Ultrafast Ultrasound Imaging, Animal model
319

Pathogenic mechanisms of clinical S. aureus isolates to induce infective endocarditis

Christian Schwarz1, Yasemin Töre1, Cornelius Faber1, Silke Niemann2, Verena Hoerr1, 3

1 University Hospital Muenster, Department of Clinical Radiology, Münster, Germany
2 University Hospital Muenster, Institute of Medical Microbiology, Münster, Germany
3 University Hospital Jena, Institute of Medical Microbiology, Jena, Germany

Introduction

Staphylococcus aureus-induced infective endocarditis (IE) is a life threatening disease[1]. To identify the key virulence factors for the induction and progression of IE, several previous studies on the pathomechanisms have been performed with different knock-out mutants[2]. However, to analyze whole virulence strategies investigations of clinical isolates are needed. To this end, we established a strain collection of 20 clinical endocarditis isolates, characterized their manifestation in a mouse model of IE by MRI and determined their invasive, proinflammatory and cytotoxic features [Fig.1].

Methods

Mouse model: In C57Bl/6 mice, an irritation of the aortic valves was induced by placing a 32G catheter at the aortic root, followed by an infection with S. aureus (105 colony-forming units (CFU)) 24h post surgical intervention.
Imaging: 24h post infection animals were investigated by MRI at 9.4T (Biospec 94/20, Bruker), using a self-gated cardiac ultra-short echo time (UTE) sequence (TR/TE, 5/0.31ms; in-plane/slice, 0.125/1mm; duration: 12:08min) [3].
Ex vivo analysis: After MRI measurements, mice were sacrificed, organs (heart, lung, spleen, kidneys, liver, aortic valves, aortic arch) were homogenized and plated on blood agar, to count the bacterial load.
In vitro analysis: From all clinical isolates, cell death, invasion and S. aureus-platelet associates were analyzed by flow cytometry.

Results/Discussion

Clinical strains were screened for key pathogenic features in infection development (e.g. bacteria-platelet associates, cell invasion, cytotoxicity). Three of the strains isolated from acute and subacute IE showed substantial differences in the pathogenic patterns: Strain 33 revealed a strong induction of platelet associates (34.11±3.45u/ml), strain 17 resulted in high levels of bacteria-platelet associates (32.09±8.53%) together with high cell invasion and cytotoxicity while strain 30 (12.91±4.73u/ml) showed only moderate degrees of all three characteristics. For all 3 strains, pronounced S. aureus vegetations on the aortic valves were identified in vivo by MRI, macroscopic analysis and CFU counts (Fig. 2). Strain 33 showed the highest CFU counts on the valves as well as in all other organs (area under the curve (AUC=17.7;n=6), followed by strain 17 (AUC=16.4;n=8) and 30 (AUC=10.3;n=9), reflecting the importance of bacteria-platelet associates and cytotoxicity in the formation of IE.

Conclusions

• Cardiac MRI gives the first hint to pathophysiological processes of IE.
• Additional in vitro analysis of the bacterial strains provides a comprehensive insight into the pathomechanisms of S. aureus infections.
• Binding of bacteria to activated platelets and host cell invasion are the most prominent pathological pathways to induce fulminant IE with high bacterial counts on the aortic valves both in humans and mice.

References
[1] Lowy, F.D. (1998). N. Engl. J. Med. 339:520-532
[2] Liesenborghs L et al. (2019). Eur. Heart J. 0, 1–12
[3] Ring J et al. (2014). PLoS ONE 9(9): e107179.
Workflow of the in vitro and in vivo screening.

Fig. 1: Workflow of the in vitro and in vivo screening of clinical S. aureus isolates. Red arrows point at S. aureus infection.

Results of the in vivo and in vitro characterization.
Fig. 2: In vivo and in vitro characterization of clinical S. aureus isolates A: In vivo MRI and macroscopic ex vivo imaging of infected aortic valves. B: In vitro analysis of the key pathogenic features such as bacteria-platelet associates, cell invasion and cytotoxicity. C: Bacterial counts of infected organs.

 

Keywords: endocarditis, S. aureus, infection imaging, pathomechanism, clinical isolates
320

Non-invasive imaging of mitochondrial dysfunction and anthracycline cardiotoxicity by repurposing 99mTc-Sestamibi SPECT imaging

Friedrich Baark1, 2, Edward C. T. Waters1, Melissa Gargaro1, Thomas Eykyn1, Richard Southworth1

1 King's College London, Imaging Chemistry & Biology, London, United Kingdom
2 King's College London, Cardiovascular Medicine, London, United Kingdom

Introduction

Anthracyclines are a first in line therapy used to treat numerous forms of cancer. However, they are highly toxic to the heart, inducing coronary heart disease, cardiomyopathy, and heart failure. Cardiotoxicity limits chemotherapeutic dose, and can develop years or decades after therapy. During the latency period, cardiotoxicity is only monitored clinically by evaluating changes in cardiac structure and contractility, which are not sensitive enough for meaningful intervention. We are developing nuclear imaging approaches to probe mitochondrial function as predictors of evolving cardiotoxicity.

Methods

We have developed a chronic model of cardiotoxicity using 6-8 week old Wistar rats (Charles River, UK) which were subcutaneously implanted with osmotic minipumps loaded with either saline, doxorubicin, or doxorubicin co-loaded with the iron chelator deferiprone. The minipumps infused their contents into the animals for a 4 week period, which was followed by a further 4 week period to allow the injury to develop. Baseline echocardiography was performed to establish normal cardiac function in all animals, followed by serial echocardiography measurements throughout the protocol to monitor any changes in cardiac function and morphology.  At the 8 week endpoint SPECT imaging and organ biodistribution with 99mTc-Sestamibi was performed and a panel of biomarkers of interest were examined.

Results/Discussion

In an in vivo rat model of chronic cardiotoxicity we show dose-dependent loss of cardiac MIBI retention before any detectable changes in cardiac function. Cardiac MIBI retention decreased from 1.4%±0.1 (injected dose per gram) in control animals to 0.79%±0.08 with our top dose of doxorubicin. We have also go on to show that a co-infusion of doxorubicin with the iron chelator deferiprone limits anthracycline cardiotoxicity and mitochondrial iron overload, and restores cardiac MIBI retention (increasing from 0.79%±0.08 with doxorubicin alone to 1.2%±0.2 in the Deferiprone group). Average cardiac p38 expression was higher in the 10 mg/kg group than vehicle and 2 mg/kg, as well as the 10 mg/kg deferiprone group. Mitochondrial iron was higher in the 10 mg/kg group than all other groups, and lower in the deferiprone treated group, and cardiac sestamibi retention decreased in a doxorubicin-dependent manner, and was closer to control values in the 10 mg/kg group co-treated with deferiprone.

Conclusions

We believe the data gathered thus far demonstrates the potential of 99mTc-Sestamibi imaging as an early readout of evolving cardiotoxicity and as a means of evaluating novel cardioprotectant strategies. Furthermore, we believe this study shows that iron chelation therapy has potential as a cardioprotective strategy for patients receiving anthracycline treatment.

References
[1] McGowan JV, Chung R, Maulik A, Piotrowska I, Walker JM, Yellon DM. Anthracycline Chemotherapy and Cardiotoxicity. Cardiovascular drugs and therapy. 2017;31(1):63-75.
Figure 2. Correlation between biomarkers of anthracycline cardiotoxicity

A) Mitochondrial iron II vs phosphorylated p38 levels B) Mitochondrial iron II vs cardiac retention of 99mTc-Sestamibi, C) phosphorylated p38 levels vs. cardiac retention of 99mTc-Sestamibi Data represents mean ± SD (n=6).

Figure 1. Schematic of osmotic minipump.
A schematic of the components of the osmotic minipump used in experiments.
Keywords: Anthracyclines, cardiotoxicity, mitochondria, oncocardiology
321

Overexpression of the adenosine A2A receptor in murine heart assessed by PET imaging with [18F]FLUDA

Daniel Gündel1, Thu Hang Lai1, Sladjana Dukic-Stefanovic1, Magali Toussaint1, Winnie Deuther-Conrad1, Rodrigo Teodoro1, Peter Boknik1, Ulrich Gergs3, Joachim Neumann3, Peter Brust1

1 Helmholtz Zentrum Dresden-Rossendorf, Institute for Radiopharmaceutical Cancer Research, Dept. for Neuroradiopharmaceuticals, Leipzig, Germany
2 Martin-Luther-University Halle-Wittenberg, Medical Faculty, Institute for Pharmacology and Toxicology, Halle (Saale), Germany

Introduction

The impact of adenosine A2A receptors (A2AR) in heart diseases is discussed diversely and only a few preclinical models are available. Therefore, we generated a transgenic mouse (TG) model with heart-specific overexpression of the human A2AR (hA2AR). The overexpressed hA2AR exhibited a cardioprotective, but proarrhythmic function, and A2AR agonists exerted a positive inotropic effect in vitro [1, 2]. Here, we show, that our new radioligand [18F]FLUDA can be used to assess hA2AR overexpression in murine heart by PET and to proof specific A2AR binding in human atrial samples by autoradiography.

Methods

FVB/N mice overexpressing the hA2AR under control of a α-MHC promotor were studied. Receptor autoradiography was used to determine Kd and Bmax of [18F]FLUDA in hearts of WT and TG mice (n=3). A 90 min dynamic µPET acquisition was performed to determine the biodistribution of [18F]FLUDA (7.4±3.4 MBq i.v.; Am=23-154 GBq/µmol) in wildtype (WT) and TG (n=3-5) after preinjection of vehicle or the A2AR antagonist tozadenant (2.5 mg/kg bw). The PET images were attenuation corrected by a T1-weighted MRI and list mode data were reconstructed (dynamic, 3D-OSEM algorithm). For activity quantification in tissues VOIs were determined by MRI images (Fig. 2A). In addition, the impact of 1µM FLUDA on the force of contraction (FOC) in isolated electrically driven atrial preparation was investigated.

Results/Discussion

In vitro autoradiography of [18F]FLUDA in cryosections of hearts (Fig. 1) revealed a KD of 5.9 ± 1.6 nM and Bmax of 455 ± 78 fmol/mg protein in TG, whereas in WT the receptor density was too low for exact quantification. Using ZM241385 as competitor 36.3 ± 5.3 % specific binding of [18F]FLUDA was demonstrated in normal human atrial samples. PET/MR analyses revealed a 26 % (p<0.05) higher SUV ratio (SUVR) of myocard/blood (Fig.2B) in TG vs. WT mice. In TG mice the SUVR was reduced by tozadenant pre-treatment by 6 % (p<0.05) while no change in WT was observed. In electrically driven atrial preparations of TG (but not WT), FLUDA reduced the increase of FOC after CGS 2180 stimulation by about 20% (p<0.05), indicating a functional antagonism of FLUDA at the human cardiac A2AR.

Conclusions

FVB/N mice overexpressing the hA2AR are a useful model for non-invasive investigation of this receptor function with [18F]FLUDA PET. The demonstration of specific radiotracer binding in the human heart provides evidence that [18F]FLUDA might be a suitable radiotracer for assessment the A2AR status of human heart with PET. Our next steps will focus on the disease-related changes of the A2AR expression in human atrial samples with [18F]FLUDA.

Acknowledgment

The authors thank the European Regional Development Fund and Sächsische Aufbaubank (SAB) for financial support (project no. 100226753).

References
[1] Boknik, P, Drzewiecki, K, et al. 2018 , ‘Phenotyping of mice with heart specific overexpression of A2A-adenosine receptors: Evidence for cardioprotective effects of A2A-adenosine receptors.’, Front Pharmacol, 9, 1-12
[2] Bokink, P, Drzewiecki K, et al. 2019, ‘Evidence for arrhythmogenic effects of A2A-adenosine receptors.’, Front Pharmacol, 10, 1-12
Fig. 1
Representative autoradiography of 20 µm cryosections of a FVB/N mouse heart overexpressing the human adenosine A2AR (A2AR-TG), showing the total binding of [18F]FLUDA (left) and the non-homologous competition of [18F]FLUDA with the A2AR specific antagonist ZM241385 (right).
Fig. 2
A) Representative MR image (left), PET image (middle) and merged overlay (right) of one slice in the short axis orientation of TG mouse heart used for the determination of VOIs.; B) standardized uptake value ratio (SUVR) of myocard over blood under baseline (veh – vehicle) and blocking conditions (toz- tozadenant) in wildtype (WT) and myocard specific hA2AR overexpressing mice (TG); n=3-5, *p≤0.05 WT vs. TG and #p≤0.05 veh vs. toz
Keywords: [18F]FLUDA, adenosine, A2AR, heart
322

[68Ga]Ga-DOTA-Siglec-9 PET Imaging Detects Autoimmune Myocarditis in Rats

Arghavan Jahandideh1, Mia Ståhle1, Xiang-Guo Li2, Heidi Liljenbäck1, 3, Olli Moisio1, Sirpa Jalkanen4, Juhani Knuuti1, 2, Antti Saraste1, 5, Anne Roivainen1, 3

1 University of Turku & Turku University Hospital, Turku PET Centre, Turku, Finland
2 Åbo Akademi University, Turku PET Centre, Turku, Finland
3 University of Turku, Turku Center for Disease Modeling, Turku, Finland
4 University of Turku, MediCity Research Laboratory and Institute of Biomedicine, Turku, Finland
5 Turku University Hospital and University of Turku, Heart Center, Turku, Finland

Introduction

PET/CT imaging with 18F-FDG is a non-invasive tool for the detection of cardiac sarcoidosis, but it has limited specificity for myocardial inflammation due to physiological uptake in myocardium. Sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) is a leukocyte ligand of vascular adhesion protein 1 (VAP-1) which migrates to the endothelial cell surface upon inflammation. Radiolabeled Siglec-9 has been used for PET/CT imaging of inflammation and cancer [1,2]. In this study, we evaluated whether [68Ga]Ga-DOTA-Siglec-9 detects inflammation in the heart of autoimmune myocarditis rats.

Methods

Rats (n=6) were immunized twice on day 0 and 7 with subcutaneous injection of porcine cardiac myosin in an equal volume of complete Freund’s adjuvant supplemented with mycobacterium tuberculosis and i.p. pertussis toxin injection. Control rats (n=3) were injected with complete Freund’s adjuvant alone. Thirty min static PET/CT imaging at 30-60 min after i.v. [68Ga]Ga-DOTA-Siglec-9 (49.3 ± 2.3 MBq) injection was performed in rats on day 21 post-immunization followed by autoradiography and histological analysis of excised heart.

Results/Discussion

Five out of 6 immunized rats developed focal myocardial inflammatory lesions. Autoradiography of myocardial tissue sections showed co-localization of [68Ga]Ga-DOTA-Siglec-9 uptake and inflammatory lesions (Figure 1A, red arrows). PET/CT imaging with [68Ga]Ga-DOTA-Siglec-9 demonstrated higher target-to-background ratio (SUVmean myocardium/SUVmean blood) in rats with inflammatory lesions as compared with control rats (2.0 ± 0.6 vs. 0.8 ± 0.1, respectively; P = 0.02; Figure 1B,C).

Conclusions

Myocardial [68Ga]Ga-DOTA-Siglec-9 uptake is increased in autoimmune myocarditis suggesting that molecular imaging of VAP-1 is a potential approach to detect active myocardial inflammation.

AcknowledgmentThe authors would like to thank Aake Honkaniemi, Marja-Riitta Kajaala and Erica Nyman (Histology Core, Institute of Biomedicine, University of Turku) for their assistance.
References
[1] Aalto et al. Blood 2011;118:3725-3733.
[2] Virtanen et al. Arthritis Res Ther. 2015;17:308.
Figure 1

(A) An inflammatory myocardial lesion in a rat with autoimmune myocarditis identified by hematoxylin and eosin (H&E) staining and ex vivo autoradiography of [68Ga]Ga-DOTA-Siglec-9 uptake (Red arrows). (B) In vivo PET/CT images with [68Ga]Ga-DOTA-Siglec-9 in a rat with autoimmune myocarditis. PET/CT images at 30-60 min show focal tracer uptake (Red arrows) in the myocardium. (C) Target-to-background ratio (SUVmean myocardium/SUVmean blood) in immunized and control rats.

Keywords: VAP-1, Positron emission tomography, Myocarditis, Experimental autoimmune myocarditis
323

The levels of oxidative and nitrosative stress in patients who had 99mTc-MIBI myocardial perfusion scintigraphy and 99mTc-DMSA,99mTc-MAG-3 renal scintigraphy

Ebru Salmanoglu1, Ergul Belge Kurutas2

1 Kahramanmaras Sutcu Imam University, Faculty of Medicine, Department of Nuclear Medicine, Kahramanmaras, Turkey
2 Kahramanmaras Sutcu Imam University, Faculty of Medicine, Department of Medical Biochemistry, Kahramanmaras, Turkey

Introduction

Ionizing radiation is strong stimulator of reactive oxygen and nitrogen species. These reactive species may cause oxidative and nitrosative stress. In this study, we aimed to evaluate possible effects of 99mTechnetium (99mTc)-methoxyisobuthylisonitrite (MIBI), 99mTc-dimercaptosuccinic acid (DMSA), 99mTc-mercaptoacetyltriglycine (MAG-3) on oxidative and nitrosative stress biomarkers in patients who were performed myocardial perfusion scintigraphy (MPS) and renal scintigraphy.

Methods

Patients (n=29) who were referred to nuclear medicine department were chosen as the patient group.They were divided into three subgroups according to the type of disease and 99mTc labeled agent. First group had MPS (n=9).Second group had 99mTc-DMSA renal scintigraphy (n=12).Third group had 99mTc-MAG-3 renal scintigraphy (n=8). The blood samples were taken from first,second and third group 1h,3h,45min after injection of agent, respectively. The samples were taken from healty volunteers(n=25) as a control group.Alterations in both catalase(CAT),superoxide dismutase(SOD), malondialdehyde(MDA) levels as oxidative stress biomarkers and nitric oxide(NO) and 3-Nitrotyrosine(3-NTx) levels as nitrosative stress biomarkers in all blood samples were evaluated.

Results/Discussion

Results of MPS and renal scintigraphy performed patients were compared with control group separately. CAT, SOD, MDA, NO, 3-NTx levels were higher in first group than control group. However,CAT and SOD levels were lower in second and third groups than control group. MDA,NO,3-NTx levels were higher in second and third groups than control group. Our results showed that shortly after ionizing radiation exposure cellular protective pathways are triggered to overcome radiation induced reactive oxygen and nitrogen species. Our findings are in agreement with our previously reports that ionizing radiation increases both oxidative and nitrosative stress parameters in patients who undergone thyroid scintigraphy and bone scintigraphy.

Conclusions

These results show that oxidative and nitrosative balance is impaired due to ionization radiation. These reactive species might stimulate adaptive and protective cellular defense mechanism in irradiated cells soon after exposuring to radiation. Thereby, this mechanism protect organism from effects of low dose ionizing radiation.

References
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Keywords: ionizing radiation, oxidative stress, nitrosative stress, Tc-99m