Labeling of Porcine Mesenchymal Stem Cells (MSCs) with MRI contrast agent Ferex for use in Abdominal Aortic Aneurysm (AAA) Models

Abstract

IntroductionReliable methods of labeling and tracking MSCs are necessary to allow non‐invasive evaluation of their effects on aneurysm. Ferex is a super paramagnetic iron compound that when placed intracellularly, can be identified by magnetic resonance imaging (MRI). This study aims to evaluate Ferex as an in vivo cellular label in Porcine AAA models.MethodsMSCs were isolated from the pig's bone marrow via ficoll plaque separation and expanded in culture. MSCs were incubated with 100ug/ml conc. of Ferex and a cationic transfecting agent, Poly‐L‐Lysine (PLL). Around 10 million Ferex labeled MSCs were then transplanted to the pig after a surgery that induced AAA. MRI was performed at 3 Tesla three times over a two week time period post surgery at day 4, 7 and 14 respectively. A longitudinal survey scan was performed to locate the AAA within the tissue. Time‐of‐Flight (TOF) and T2 weighted images were obtained to evaluate the vasculature and flow with in the AAA as well as to identify the iron laden cells within the arterial wall. Following the T2‐weighted scan, T2*‐weighted multiple echo gradient echo sequences were applied in order to quantify the signal on a pixel‐by‐pixel basis.ResultsAs shown in Figure 1, the iron labeled cells were visible (as signal loss) at all time points post transplant. T2* values strongly indicate that the iron cores remained within the labeled stem cells (and were not exocytosed and/or phagocytosed by other cells). The percent relative change in the normal arterial wall was 0.8 +/− 2%, respectively for all time points tested. Figure 2 summarizes the results obtained from the Perl's’ staining. Strong correlation between the in vivo MR signal and iron deposition (blue color on Perl's) was observed.ConclusionThe results clearly support the hypothesis and show that it is possible to detect iron over a two week time interval post transplant accompanied by strong correlation between MR and histology.