title: Combined small interfering RNA therapy and in vivo magnetic resonance imaging in islet transplantation.
abstract: OBJECTIVE
  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).
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: 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.
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.forename: Mehmet V
authors.initials: MV
authors.lastname: Yigit
authors.forename: Zdravka
authors.initials: Z
authors.lastname: Medarova
authors.forename: Lingling
authors.initials: L
authors.lastname: Wei
authors.forename: Guangping
authors.initials: G
authors.lastname: Dai
authors.forename: Christian
authors.initials: C
authors.lastname: Schuetz
authors.forename: Anna
authors.initials: A
authors.lastname: Moore
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D015316:Genetic Therapy / Q000379:methods*; D006801:Humans; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism; D007515:Islets of Langerhans / Q000378:metabolism*; D016381:Islets of Langerhans Transplantation / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods; D051379:Mice; D016688:Mice, Inbred NOD; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D007328:Insulin; D034741:RNA, Small Interfering; D053148:Caspase 3