MRI investigation of angiogenesis after neuronal progenitor cell therapy of stroke

Introduction

Cell therapy improves functional recovery in experimental stroke ¹ , which may be related to cell therapy induced angiogenesis². In this study, we report for the first time that quantitative MRI can dynamically monitor cell mediated induction of angiogenesis.

Materials and Methods

Neural rogenitor cells were labeled by superparamagnetic particles using a biolistic device “gene gun” ¹ . Eight male Wistar rats were placed in a stereotaxic frame. 1×10⁵ superparamagnetic labeled cells were injected into the cisterna magna 48 h after stroke. MRI measurements were performed from one day before to 6 weeks after cell transplantation. Three dimensional MRI, T_1sat (T₁ in the presence of an off-resonance irradiation of the macromolecules of brain), T₁, T₂, cerebral blood floor (CBF), cerebral blood volume (CBV), and blood-to-brain transfer constant (K_i) of Gd-DTPA were used to measure migration and localization of labeled cells and to characterize biophysical changes of angiogenesis after cell therapy. To detect superparamagnetic labeled cells in the host brain and angiogenesis, brain sections were stained for iron using Prussian blue reaction, and for angiogenesis using vWF immunostaining.

Results

The labeled cells selectively migrated towards ischemic boundary regions as detected by MRI from 1 to 6 weeks after cell transplantation (Fig 1, 3D). Different temporal changes in biophysical parameters were detected between ischemic regions with and without angiogenesis. MRI revealed an increase in Ki in the angiogenic region (Fig1, K_i), which maximized at 2 weeks and returned to normal at 6 weeks. The vWF immunoreactive images showed an increase in numbers of vWF immunoreactive vessels (Fig 1). The angiogenic region exhibited increased (p<0.01) CBF and CBV compared to that in the non-angiogenic ischemic region at 6 weeks after cell therapy. The relative T_1sat and T₂ values in angiogenic region were also significantly lower (T_1sat, p<0.05 at 1 to 6 weeks and T₁, p<0.05 at 6 weeks, T₂, p<0.05 at 3 to 6 weeks) than that in the non-angiogenic ischemic region after cell therapy. Of these methods, K_i, CBF, and CBV appear most useful measurements to identify and predict angiogenic location and areas. T_1sat, T₁, and T₂ provide complimentary information to characterize ischemic tissue with and without angiogenesis.

Figure 1

Discussion

These studies show that MRI can dynamically monitor labeled cell migration, distribution and angiogenic impact on ischemic tissue. Angiogenesis after cell therapy in ischemic brain colocalizes with the distribution of implanted cells. These cells may promote angiogenesis by expressing or inducing the expression of angiogenic factors like VEGF in parenchymal tissue ² . Our data also suggest that K_i, CBF, and CBV are important methodologies for potential application to the cell therapy of stroke patients.