gms | German Medical Science

Objective: Despite many data from previous cohort studies, the absolute risk of formation and growth of intracranial aneurysms (IAs) remains uncertain. A key event in aneurysm formation and progression is the degradation of the internal elastic lamina (IEL) which prevents vessel wall distension under physiological conditions. To date no existing modality permits specific in vivo visualization and imaging of the main component of IEL, i.e. elastin, to potentially detect anatomical sites at risk for IA formation and growth. We recently facilitated radiocarbon birth dating of cerebrovascular elastin to understand elastin turnover ex vivo. Recent studies have reported the use of a new contrast agent for specific labeling of elastin in the setting of atherosclerosis. Therefore we attempted to establish a Positron Emission Tomography contrast agent for the visualization of cerebrovascular elastin in humans.

Methods: An elastin binding low molecular weight structure conjugated to NODAGA as a chelator was synthesized, purified and radiolabeled with 68Gallium (68Ga-NODAGA-molecule). We performed stability tests by analyzing the radiolabeling agent with high-performance liquid chromatography (HPLC) after exposing it to different pH, temperature conditions and human serum. Elastin and albumin – as negative controls – were incubated for 10, 30 and 60 minutes with the 68Ga-NODAGA-molecule as well as with 68Ga-NODAGA exclusively. Protein-bound radioactivity was measured by gamma counter.

Results: HPLC analysis demonstrated stability of the elastin tracer under various pH and temperature conditions. Elastin demonstrated significant more counts per minute compared to albumin after 10 and 60 minutes (t-test: 10min: p=0.01, 30min: p=0.13, 60min: p<0.001) which indicates specific binding of the elastin tracer. In confirmation of binding specificity, elastin incubated with the 68Ga-NODAGA-molecule also showed significantly higher radioactivity in comparison to elastin incubated with 68Ga-NODAGA exclusively after 60 minutes (t-test: 10min: p=0.06, 30min: p=0.07, 60min: p=0.001).

Conclusion: Our synthesized radiotracer selectively labels elastin as a protein itself in vitro. On the basis of these promising results, binding specificity will further be investigated by autoradiography after incubating sections of rat skin, cadaveric cerebral vessels and human IAs ex vivo.