MRI of Pericyte Reduction to Quantitate Diabetic Retinopathy in vivo

Diabetic retinopathy is a common and specific microvascular complication of diabetes. The ability to diabetic retinopathy in inaccessible retina would benefit both our understanding of diabetic retinal degeneration and our ability to develop appropriate therapies. We have developed a cell targeting MR contrast agent that links contrast agents with small phosphorothioate-modified antisense DNA (sODN) of 18-26 nucleotides in length to enable in vivo reporting and quantitatively charaterizing pericyte in a mouse model of cerebral ishcemia with a leaky blood brain barrier (BBB) by magnetic resonance imaging (MRI). The specificity of this novel contrast agent is mediated by retention of sODN bound to mRNA target but exclusion of free or non-targeting sODN in all living cells including multipotent PC12 cells, fresh brain slices and living mouse brains. These sODN, when labeled with superparamagnetic iron oxide nanopaticels (SPION) via NeutrAvidin-biotin linakage, can be made as multimodal for MRI in vivo and electronic microscopy (EM) ex vivo. We have several SPION-sODNs that co-register cohorts of cells with a resolution of < 0.03 mm3. These SPION-sODNs detect a wide range of physiologic and pathologic processes, such as gliogenesis, angiogenesis and leaky BBB in progress, including living C57black6 mice with compromised BBB after forebrain ischemia using bilateral carotid occlusion (BCAO). We have demonstrated delivery of our contrast agent as eye drops (Liu et al., FASEB J 22:1193, 2008). Recently, we show caveolae mediates the uptake of SPION-sODN after non-invasive intraperitoneal (i.p.) injection; SPION-sODN reports mRNA expression with a positive correlation (R2 = 1.0, p = 0.02) between the elevation in the rate of MR signal reduction (DR2*) value above the baseline (in vivo) and mRNA copy number (ex vivo TaqMan analysis.