Quantitative magnetic resonance imaging of enzyme activity on the cell surface: in vitro and in vivo monitoring of ADP-ribosyltransferase 2 on T cells.
The objective of this study was to quantify enzymatic activity on the surface of T cells by magnetic resonance imaging (MRI) using R2 and R2* relaxometry. Lymphoma cells expressing adenosine diphosphate (ADP)-ribosyltransferase 2 (ART2) were incubated with increasing doses of its substrate etheno-nicotinamide adenine dinucleotide (NAD), resulting in increasing amounts of surface protein ADP-ribosylation. Etheno-ADP-ribosylated proteins were detected with monoclonal antibody 1G4 and superparamagnetic iron oxide conjugated secondary antibodies (Ab-SPIO). Labeling efficiency was determined with R2 and R2* relaxometry on a clinical 3.0 T scanner. Parallel aliquots of cells were analyzed by flow cytometry. Cell-bound SPIO conjugates were detected by immunofluorescence and electron microscopy and quantified by atomic absorption spectroscopy. To mimic an inflammatory site in vivo, Ab-SPIO-labeled cells were injected subcutaneously in mice and analyzed by MRI. Immunofluorescence and electron microscopy confirmed cell-surface localization of Ab-SPIO. MRI of Ab-SPIO-labeled cells showed a corresponding signal reduction. Increases in R2 and R2* determined by magnetic resonance relaxometry correlated linearly with the expression level of ART2 and the concentration of the ART2 substrate etheno-NAD. R2 and R2* increases correlated linearly with the results from flow cytometry and atomic absorption spectroscopy analyses. Quantitative R2 and R2* mapping enable noninvasive determination of enzymatic activity on T cells and holds promise for characterization of inflammatory sites in vivo by MRI.
Bannas
Peter
P
Department of Diagnostic and Interventional Radiology and Institute of Immunology, University Medical Center, Hamburg-Eppendorf, Germany. p.bannas@uke.uni-hamburg.de
Graumann
Oliver
O
Balcerak
Philipp
P
Peldschus
Kersten
K
Kaul
Michael Gerhard
MG
Hohenberg
Heinrich
H
Haag
Friedrich
F
Adam
Gerhard
G
Ittrich
Harald
H
Koch-Nolte
Friedrich
F
D036002:ADP Ribose Transferases / Q000378:metabolism*; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology*; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism*; D005434:Flow Cytometry; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051379:Mice; D008807:Mice, Inbred BALB C; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D009243:NAD / Q000378:metabolism / Q000494:pharmacology; D015203:Reproducibility of Results; D013601:T-Lymphocytes / Q000201:enzymology*; D051598:Whole Body Imaging
D000911:Antibodies, Monoclonal; D005290:Ferric Compounds; D009243:NAD; C000499:ferric oxide; D000246:Adenosine Diphosphate Ribose; D036002:ADP Ribose Transferases