BACKGROUND: In vitro labelling of cells and small cell structures is a necessary step before in vivo monitoring of grafts. We modified and optimised a procedure for pancreatic islet labelling using bimodal positively charged poly(lactic-co-glycolic acid) nanoparticles with encapsulated perfluoro crown ethers and indocyanine green dye via microporation and compared the method with passive endocytosis. RESULTS: Pancreatic islets were microporated using two pulses at various voltages. We tested a standard procedure (poration in the presence of nanoparticles) and a modified protocol (pre-microporation in a buffer only, and subsequent islet incubation with nanoparticles on ice for 10 min). We compared islet labelling by microporation with labelling by endocytosis, i.e. pancreatic islets were incubated for 24 h in a medium with suspended nanoparticles. In order to verify the efficiency of the labelling procedures, we used 19F magnetic resonance imaging, optical fluorescence imaging and confocal microscopy. The experiment confirmed that microporation, albeit fast and effective, is invasive and may cause substantial harm to islets. To achieve sufficient poration and to minimise the reduction of viability, the electric field should be set at 20 kV/m (two pulses, 20 ms each). Poration in the presence of nanoparticles was found to be unsuitable for the nanoparticles used. The water suspension of nanoparticles (which served as a surfactant) was slightly foamy and microbubbles in the suspension were responsible for sparks causing the destruction of islets during poration. However, pre-microporation (poration of islets in a buffer only) followed by 10-min incubation with nanoparticles was safer. CONCLUSIONS: For labelling of pancreatic islets using poly(lactic-co-glycolic acid) nanoparticles, the modified microporation procedure with low voltage was found to be safer than the standard microporation procedure. The modified procedure was fast, however, efficiency was lower compared to endocytosis.

Centre of Experimental Medicine Institute for Clinical and Experimental Medicine Vídeňská 1958 9 Prague Czech Republic

Department of Tissue Culture and Stem Cells Institute of Experimental Medicine AS CR Vídeňská 1083 142 20 Prague Czech Republic

Department of Tumor Immunology Radboud University Medical Centre Route 278 Geert Grooteplein 28 Nijmegen Netherlands

Diabetes Centre Institute for Clinical and Experimental Medicine Vídeňská 1958 9 Prague Czech Republic

MR Unit Radiodiagnostic and Interventional Radiology Department Institute for Clinical and Experimental Medicine Vídeňská 1958 9 Prague Czech Republic

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Cationic fluorinated micelles for cell labeling and 19F-MR imaging

A Trimodal Imaging Platform for Tracking Viable Transplanted Pancreatic Islets In Vivo: F-19 MR, Fluorescence, and Bioluminescence Imaging