Combined Small Interfering RNA Therapy and In Vivo Magnetic Resonance Imaging in Islet Transplantation

Molecular Imaging Laboratory, MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Diabetes (Impact Factor: 8.1). 02/2011; 60(2):565-71. DOI: 10.2337/db10-1400
Source: PubMed

ABSTRACT Recent advances in human islet transplantation are hampered by significant graft loss shortly after transplantation and inability to follow islet fate directly. Both issues were addressed by utilizing a dual-purpose therapy/imaging small interfering RNA (siRNA)-nanoparticle probe targeting apoptotic-related gene caspase-3. We expect that treatment with the probe would result in significantly better survival of transplanted islets, which could be monitored by in vivo magnetic resonance imaging (MRI).
We synthesized a probe consisting of therapeutic (siRNA to human caspase-3) and imaging (magnetic iron oxide nanoparticles, MN) moieties. In vitro testing of the probe included serum starvation of the islets followed by treatment with the probe. Caspase-3 gene silencing and protein expression were determined by RT-PCR and Western blot, respectively. In vivo studies included serial MRI of NOD-SCID mice transplanted with MN-small interfering (si)Caspase-3-labeled human islets under the left kidney capsule and MN-treated islets under the right kidney capsule.
Treatment with MN-siCaspase-3 probe resulted in decrease of mRNA and protein expression in serum-starved islets compared with controls. In vivo MRI showed that there were significant differences in the relative volume change between MN-siCaspase-3-treated grafts and MN-labeled grafts. Histology revealed decreased caspase-3 expression and cell apoptosis in MN-siCaspase-3-treated grafts compared with the control side.
Our data show the feasibility of combining siRNA therapy and in vivo monitoring of transplanted islets in mice. We observed a protective effect of MN-siCaspase-3 in treated islets both in vitro and in vivo. This study could potentially aid in increasing the success of clinical islet transplantation.

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    • "The synthesized probe consisted of magnetic dextran-coated iron oxide MNs labeled with Cy5.5 near-infrared optical dye and conjugated to siRNA at the dextran surface. First, we synthesized Cy5.5-labeled MNs, as previously reported (27). Briefly, a solution of monoactivated Cy5.5 succinimide ester (Amersham Biosciences, Piscataway, NJ) in 20 mmol/L sodium citrate and 0.15 mol/L NaCl was reacted with previously dialyzed immunopure, aminoderivatized dextran-coated iron oxide (pH 8.5) with constant agitation for 12 h at room temperature. "
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    • "A more recent study by our group used a dual-purpose therapy/imaging nanoparticle probe to target the apoptotic-related gene caspase-3. We demonstrated that our “two-in-one” MN-siCaspase-3 imaging probe could silence the apoptotic-related gene, providing significant protection to the grafts from early loss after transplantation, and at the same time served as an MRI label to assess the in vivo post-transplant fate of the grafts noninvasively (Figure 3) [24, 91]. The results of our study are in line with those of another recently published study showing that the use of fluorinated alginate microcapsules increased the insulin secretion rate of human islets and at the same time allowed detection by MRI and CT imaging [94]. "
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