Imaging of αvβ3 integrin expression in experimental myocardial ischemia with [68Ga]NODAGA-RGD positron emission tomography

Abstract

Background: Radiolabeled RGD peptides detect αvβ3 integrin expression associated with angiogenesis and extracellular matrix remodeling after myocardial infarction. We studied whether cardiac positron emission tomography (PET) with [68Ga]NODAGA-RGD detects increased αvβ3 integrin expression after induction of flow-limiting coronary stenosis in pigs, and whether αvβ3 integrin is expressed in viable ischemic or injured myocardium.

Methods: We studied 8 Finnish landrace pigs 13 ± 4 days after percutaneous implantation of a bottleneck stent in the proximal left anterior descending coronary artery. Antithrombotic therapy was used to prevent stent occlusion. Myocardial uptake of [68Ga]NODAGA-RGD (290 ± 31 MBq) was evaluated by a 62 min dynamic PET scan. The ischemic area was defined as the regional perfusion abnormality during adenosine-induced stress by [15O]water PET. Guided by triphenyltetrazolium chloride staining, tissue samples from viable and injured myocardial areas were obtained for autoradiography and histology.

Results: Stent implantation resulted in a partly reversible myocardial perfusion abnormality. Compared with remote myocardium, [68Ga]NODAGA-RGD PET showed increased tracer uptake in the ischemic area (ischemic-to-remote ratio 1.3 ± 0.20, p = 0.0034). Tissue samples from the injured areas, but not from the viable ischemic areas, showed higher [68Ga]NODAGA-RGD uptake than the remote non-ischemic myocardium. Uptake of [68Ga]NODAGA-RGD correlated with immunohistochemical detection of αvβ3 integrin that was expressed in the injured myocardial areas.

Conclusions: Cardiac [68Ga]NODAGA-RGD PET demonstrates increased myocardial αvβ3 integrin expression after induction of flow-limiting coronary stenosis in pigs. Localization of [68Ga]NODAGA-RGD uptake indicates that it reflects αvβ3 integrin expression associated with repair of recent myocardial injury.

Keywords: Angiogenesis; Myocardial ischemia; Positron emission tomography; αvβ3 integrin.

Figures

Fig. 1

Co-registration of [68Ga]NODAGA-RGD and [15O]water PET images and definition of myocardial contours. a and f demonstrate [68Ga]NODAGA-RGD images during the first 2 min after injection of the tracer, b and g demonstrate the fusion of [15O]water PET images (c, h) and [68Ga]NODAGA-RGD images used in the co-registration (a, f). Yellow lines represent myocardial contours defined in [15O]water PET images and copied to the [68Ga]NODAGA-RGD images. d and i demonstrate the fusion of the [15O]water PET images (c, h) and [68Ga]NODAGA-RGD images during the last 20 min of the imaging session (e, j) that demonstrate higher activity in the ischemic area in the anteroseptal wall as compared with the remote myocardium in the inferoposterior wall

Fig. 2

Cardiac [68Ga]NODAGA-RGD and [15O]water in vivo PET analyses. a and b demonstrate polar maps of MBF measured by [15O]water PET at rest and during adenosine stress, respectively. c and d show polar maps of [68Ga]NODAGA-RGD uptake. Note the presence of increased [68Ga]NODAGA-RGD uptake in c co-localizing with an area of reduced myocardial perfusion (asterisk in a, b) as compared with the remote area (arrowhead in a, b). Distribution of [68Ga]NODAGA-RGD is homogenous in the left ventricle of sham operated pig (d)

Fig. 3

Myocardial histology. Left panel representative image of 2,3,5-triphenyltetrazolium chloride (TTC) staining. The arrows show the areas where the tissue samples of the injured area, viable ischemic area and remote area were collected. a–o demonstrate stainings of hematoxylin-eosin (a–c) and Masson’s trichrome (d–f), and immunohistochemical stainings of CD31 (g–i), αvβ3 integrin (j–l) and α-smooth muscle actin (m–o), and autoradiography (p–r) from the remote myocardium, from the viable ischemic area or injured myocardium based on TTC staining. Scale bar 50 µm

Fig. 4

Immunohistochemistry of endothelial cells and αvβ3 integrin. The graphs in a and b show areal percentages of myocardium stained with CD31 antibodies (endothelial cells) and αvβ3 integrin antibodies, respectively. Integrin αvβ3 staining correlates with the [68Ga]NODAGA-RGD uptake measured by autoradiography in the viable ischemic area, in the injured area and in the remote area (c)

Fig. 5

Kinetics [68Ga]NODAGA-RGD. Mean (n = 8) time-activity curves of average [68Ga]NODAGA-RGD uptake in the remote myocardium, in the ischemic area and in the blood from the whole imaging session (a) and from the end part of the imaging session (b)

Fig. 6

Quantification of [68Ga]NODAGA-RGD uptake. The graphs in a show [68Ga]NODAGA-RGD uptake measured in PET images in the remote myocardium and in the ischemic area. b Shows [68Ga]NODAGA-RGD uptake measured with a gamma counter (ex vivo biodistribution) in myocardial tissue samples obtained from the remote myocardium and from the viable ischemic area or injured myocardium based on TTC staining. c Shows [68Ga]NODAGA-RGD uptake by autoradiography in myocardial tissue sections in the remote myocardium, viable ischemic area or injured myocardium. n number, SUV standardized uptake value