Dr. Cees Ja Van Echteld
Dr. Hofstra from Maastricht, NL, used an integrin άvβ3 targeted tracer for evaluation of angiogenesis. However, in animal experiments, he found the tracer to bind predominantly to myofibroblasts rather than to angiogenic cells. With this tracer, he found not only uptake in infarcts but also in remote myocardium. A similar 99m-Tc labeled RGD peptide, targeted to άvβ3, was used in preliminary human studies to show uptake in infarcts, but in some patients also in remote areas.
Dr. Lindner from Portland, USA, emphasized the importance of specificity of targets, access of targets and the need for residual flow to deliver tracers. He discriminated between small diffusible, extravasating tracers and larger bloodpool tracers such as liposomes and microbubbles. Combining flow measurements and integrin ά5 targeted microbubbles proved to be a powerful tool to assess inflammation in animal models. Dr. Carr from Oxford, UK, used bone marrow derived stromal cells which took up iron oxide particles with a fluorescent coating. She demonstrated that directly transplanted cells were retained in severe infarcts, but not so in smaller infarcts in mice. Disappointingly, no evidence was found for differentiation, nor could improvement of function be demonstrated. Experiments with other cell types, e.g. cardio-sphere derived stem cells are ongoing. Dr. Bengel from Baltimore, USA, emphasized the advantages of nuclear imaging for stem cell tracking. For stem cell delivery, prior 18F-FDG labeling of the stem cells can be used but only in moderation since high levels of FDG are toxic. For long-term engraftment, a reporter gene is more appropriate. Disadvantages of this approach include transient expression, deactivation, immunogenicity and cell dysfunction, but a major advantage is that the expression of the target is directly related to cell viability. Dr. Bengel presented data on stem cells expressing human NIS (sodium-iodine symporter) using 124-I or 99m-Tc for measuring NIS activity. In animal experiments, it could be demonstrated that stem cells that were expressing NIS as well as being labeled with iron oxide particles and that immediately after transplantation both methods yielded uptake/contrast at the site of injection, but after one week only the iron oxide contrast remained, suggesting redistribution of the iron-oxide particles.
A variety of methods are available for stem cell tracking in vivo. However, these methods have only been demonstrated in animal experiments and are less suitable for use in human studies. So far no suitable method for in vivo imaging of angiogenesis is available.
In vivo imaging for cardiac regeneration
This congress report accompanies a presentation given at the ESC Congress 2008. Written by the author himself/herself, this report does not necessarily reflect the opinion of the European Society of Cardiology.
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