PET imaging of ischaemic myocardial injury and angiogenesis

The myocardium of patients with coronary artery disease (CAD) often is a mixture of ischaemic but viable tissue and irreversibly injured scar tissue. The viable tissue has capability of functional recovery after restoration of blood flow and the assessment of myocardial viability is important in identifying patients who will most likely benefit from revascularisation. Angiogenesis is an essential part of the healing process after ischaemic myocardial injury aiming at restoration of intact tissue capillary network. Measurement of myocardial blood flow by positron emission tomography (PET) and [15O]water is widely used in the evaluation of CAD, but its value in the assessment of myocardial viability is incompletely understood. [68Ga]NODAGA-RGD is a novel PET tracer binding to αvβ3 integrin that plays a central role in angiogenesis and therefore, may enable imaging of angiogenic activity. The purpose of this thesis was to evaluate [15O]water and [68Ga]NODAGA-RGD for the assessment of myocardial viability and ischaemic myocardial injury by PET in experimental models. We used pig models of surgically or percutaneously induced coronary stenosis and human cell based in vitro model of angiogenesis. In the first substudy, we found that resting myocardial blood flow (MBF), perfusable tissue fraction (PTF) and perfusable tissue index (PTI) by [15O]water PET detected myocardial viability with good accuracy in pig models of ischaemic heart failure and myocardial ischaemia. In the second substudy, we found that [68Ga]NODAGA-RGD demonstrated increased myocardial αvβ3 integrin expression in the ischaemic myocardium that was localised in the irreversibly injured myocardium. In the third substudy, we found that the uptake of [68Ga]NODAGA-RGD was proportional to angiogenic activity in an in vitro angiogenesis tissue model. In conclusion, these experimental studies indicate that resting MBF, PTF and PTI by [15O]water PET are useful indexes of myocardial viability in chronic CAD. [68Ga]NODAGA-RGD PET may be useful for the identification of αvβ3 integrin activation associated with recent ischaemic myocardial injury. This tracer reflects angiogenetic activity in vitro, but its specificity for angiogenesis in vivo remains uncertain.Sydänlihaksen iskeemisen vaurion ja uudisverisuonituksen PET kuvantaminen Sepelvaltimotautipotilaiden sydänlihas koostuu usein iskeemisestä, mutta elinkykyisestä ja peruuttamattomasti vaurioituneesta kudoksesta. Elinkykyisen sydänlihaksen toiminta voi palautua normaaliksi verenkierron palauttamisen jälkeen, ja elinkykyisyyden arviointi on tärkeää verenkierron palauttamisesta hyötyvien potilaiden tunnistamisessa. Uudisverisuonitus eli angiogeneesi, jonka tarkoitus on palauttaa kudokseen toimiva hiussuoniverkosto, on tärkeä osa iskeemisen vaurion jälkeistä paranemista. Sydänlihaksen verenvirtauksen mittaaminen positroniemissiotomografialla (PET) käyttäen merkkiaineena [15O]vettä on paljon käytetty menetelmä sydäntaudin arvioinnissa, mutta sen soveltuvuutta sydänlihaksen elinkykyisyyden arviointiin ei tiedetä. [68Ga]NODAGA-RGD on uusi angiogeneesiä säätelevään αvβ3 integriiniin sitoutuva merkkiaine jonka avulla voitaisi mahdollisesti kuvantaa sydänlihaksen angiogeenistä aktiivisuutta. Väitöskirjatyön tarkoituksena oli arvioida [15O]vesi ja [68Ga]NODAGA-RGD PET:n käyttökelpoisuutta sydänlihaksen elinkykyisyyden ja iskeemisen sydänlihasvaurion tunnistamisessa kokeellisilla malleilla. Käytimme sikoja, joille oli aiheutettu sepelvaltimotukos kirurgisesti tai katetrisaatiolla, sekä ihmissolupohjaista kokeellista angiogeneesin kudosmallia. Ensimmäisessä osatyössä havaitsimme, että [15O]vesi PET:n tehokkuus elinkykyisyyden havaitsemisessa iskeemisen sydämen vajaatoiminnan ja sydänlihasiskemian sikamalleissa oli hyvä. Toisessa osatyössä havaitsimme, että [68Ga]NODAGA-RGD:llä voitiin havaita lisääntynyt αvβ3 integriiniaktivaatio, joka sijaitsi peruuttamattomasti vaurioituneessa sydänlihaksessa. Kolmannessa osatyössä havaitsimme, että [68Ga]NODAGA-RGD:n kertymä oli verrannollinen angiogeneesiaktivaatioon kokeellisessa angiogeneesin kudomallissa. Yhteenvetona voidaan todeta, että [15O]vesi PET on käyttökelpoinen sydänlihaksen elinkykyisyyden arvioinnissa kroonisessa sepelvaltimotaudissa. [68Ga]NODAGA-RGD PET voi olla käyttökelpoinen tuoreeseen sydänlihasvaurioon liittyvän αvβ3 integriiniaktivaation kuvantamisessa. Tämä merkkiaine kuvastaa angiogeenistä aktivaatiota kokeellisesti, mutta sen tarkkuus elävässä elimistössä on epäselvää

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

Association between [Ga-68]NODAGA-RGDyK uptake and dynamics of angiogenesis in a human cell-based 3D model

Radiolabeled RGD peptides targeting expression of alpha(v)beta(3) integrin have been applied to in vivo imaging of angiogenesis. However, there is a need for more information on the quantitative relationships between RGD peptide uptake and the dynamics of angiogenesis. In this study, we sought to measure the binding of [Ga-68]NODAGA-RGDyK to alpha(v)beta(3) integrin in a human cell-based three-dimensional (3D) in vitro model of angiogenesis, and to compare the level of binding with the amount of angiogenesis. Experiments were conducted using a human cell-based 3D model of angiogenesis consisting of co-culture of human adipose stem cells (hASCs) and of human umbilical vein endothelial cells (HUVECs). Angiogenesis was induced with four concentrations (25%, 50%, 75%, and 100%) of growth factor cocktail resulting in a gradual increase in the density of the tubule network. Cultures were incubated with [Ga-68]NODAGA-RGDyK for 90 min at 37 degrees C, and binding of radioactivity was measured by gamma counting and digital autoradiography. The results revealed that tracer binding increased gradually with neovasculature density. In comparison with vessels induced with a growth factor concentration of 25%, the uptake of [Ga-68]NODAGA-RGDyK was higher at concentrations of 75% and 100%, and correlated with the amount of neovasculature, as determined by visual evaluation of histological staining. Uptake of [Ga-68]NODAGA-RGDyK closely reflected the amount of angiogenesis in an in vitro 3D model of angiogenesis. These results support further evaluation of RGD-based approaches for targeted imaging of angiogenesis

AAV2-VEGF-B gene therapy failed to induce angiogenesis in ischemic porcine myocardium due to inflammatory responses

Therapeutic angiogenesis induced by gene therapy is a promising approach to treat patients suffering from severe coronary artery disease. In small experimental animals, adeno-associated viruses (AAVs) have shown good transduction efficacy and long-term transgene expression in heart muscle and other tissues. However, it has been difficult to achieve cardiac-specific angiogenic effects with AAV vectors. We tested the hypothesis whether AAV2 gene transfer (1 x 10(13) vg) of vascular endothelial growth factor B (VEGF-B186) together with immunosuppressive corticosteroid treatment can induce long-term cardiac-specific therapeutic effects in the porcine ischemic heart. Gene transfers were delivered percutaneously using direct intramyocardial injections, improving targeting and avoiding direct contact with blood, thus reducing the likelihood of immediate immune reactions. After 1- and 6-month time points, the capillary area was analyzed, myocardial perfusion reserve (MPR) was measured with radiowater positron emission tomography ([O-15]H2O-PET), and fluorodeoxyglucose ([F-18]FDG) uptake was used to evaluate myocardial viability. Clinical chemistry and immune responses were analyzed using standard methods. After 1- and 6-month follow-up, AAV2-VEGF-B186 gene transfer failed to induce angiogenesis and improve myocardial perfusion and viability. Here, we show that inflammatory responses attenuated the therapeutic effect of AAV2 gene transfer by significantly reducing successful transduction and long-term gene expression despite the efforts to reduce the likelihood of immune reactions and the use of targeted local gene transfer methods.</p

Association between [68Ga]NODAGA-RGDyK uptake and dynamics of angiogenesis in a human cell-based 3D model

Radiolabeled RGD peptides targeting expression of αvβ3 integrin have been applied to in vivo imaging of angiogenesis. However, there is a need for more information on the quantitative relationships between RGD peptide uptake and the dynamics of angiogenesis. In this study, we sought to measure the binding of [68Ga]NODAGA-RGDyK to αvβ3 integrin in a human cell-based three-dimensional (3D) in vitro model of angiogenesis, and to compare the level of binding with the amount of angiogenesis. Experiments were conducted using a human cell-based 3D model of angiogenesis consisting of co-culture of human adipose stem cells (hASCs) and of human umbilical vein endothelial cells (HUVECs). Angiogenesis was induced with four concentrations (25%, 50%, 75%, and 100%) of growth factor cocktail resulting in a gradual increase in the density of the tubule network. Cultures were incubated with [68Ga]NODAGA-RGDyK for 90 min at 37 °C, and binding of radioactivity was measured by gamma counting and digital autoradiography. The results revealed that tracer binding increased gradually with neovasculature density. In comparison with vessels induced with a growth factor concentration of 25%, the uptake of [68Ga]NODAGA-RGDyK was higher at concentrations of 75% and 100%, and correlated with the amount of neovasculature, as determined by visual evaluation of histological staining. Uptake of [68Ga]NODAGA-RGDyK closely reflected the amount of angiogenesis in an in vitro 3D model of angiogenesis. These results support further evaluation of RGD-based approaches for targeted imaging of angiogenesis.publishedVersionPeer reviewe

Assessment of myocardial viability with [15O]water PET : A validation study in experimental myocardial infarction

BACKGROUND: Assessment of myocardial viability is often needed in patients with chest pain and reduced ejection fraction. We evaluated the performance of reduced resting MBF, perfusable tissue fraction (PTF), and perfusable tissue index (PTI) in the assessment of myocardial viability in a pig model of myocardial infarction (MI). METHODS AND RESULTS: Pigs underwent resting [15O]water PET perfusion study 12 weeks after surgical (n = 16) or 2 weeks after catheter-based (n = 4) occlusion of the proximal left anterior descending coronary artery. MBF, PTF, and PTI were compared with volume fraction of MI in matched segments as assessed by triphenyl tetrazolium chloride staining of LV slices. MBF and PTF were lower in infarcted than non-infarcted segments. Segmental analysis of MBF showed similar area under the curve (AUC) of 0.85, 0.86, and 0.90 with relative MBF, PTF, and PTI for the detection of viable myocardium defined as infarct volume fraction of &lt; 75%. Cut-off values of relative MBF of ≥ 67% and PTF of ≥ 66% resulted in accuracies of 90% and 81%, respectively. CONCLUSIONS: Our results indicate that resting MBF, PTF, and PTI based on [15O]water PET perfusion imaging are useful for the assessment of myocardial viability.Title in Web of Science: Assessment of myocardial viability with [O-15]water PET: A validation study in experimental myocardial infarction</p