title: A novel paramagnetic substrate for detecting myeloperoxidase activity in vivo.
abstract: Bis-phenylamides and bis-hydroxyindolamides of diethylenetriaminepentaacetic acid-gadolinium (DTPA(Gd)) are paramagnetic reducing substrates of peroxidases that enable molecular imaging of peroxidase activity in vivo. Specifically, gadolinium chelates of bis-5-hydroxytryptamide-DTPA (bis-5HT-DTPA(Gd)) have been used to image localized inflammation in animal models by detecting neutrophil-derived myeloperoxidase (MPO) activity at the inflammation site. However, in other preclinical disease models, bis-5HT-DTPA(Gd) presents technical challenges due to its limited solubility in vivo. Here we report a novel MPO-sensing probe obtained by replacing the reducing substrate serotonin (5-HT) with 5-hydroxytryptophan (HTrp). Characterization of the resulting probe (bis-HTrp-DTPA(Gd)) in vitro using nuclear magnetic resonance spectroscopy and enzyme kinetic analysis showed that bis-HTrp-DTPA(Gd) (1) improves solubility in water; (2) acts as a substrate for both horseradish peroxidase and MPO enzymes; (3) induces cross-linking of proteins in the presence of MPO; (4) produces oxidation products, which bind to plasma proteins; and (5) unlike bis-5HT-DTPA(Gd), does not follow first-order reaction kinetics. In vivo magnetic resonance imaging (MRI) in mice demonstrated that bis-HTrp-DTPA(Gd) was retained for up to 5 days in MPO-containing sites and cleared faster than bis-5HT-DTPA(Gd) from MPO-negative sites. Bis-HTrp-DTPA(Gd) should offer improvements for MRI of MPO-mediated inflammation in vivo, especially in high-field MRI, which requires a higher dose of contrast agent.
authors.affiliation: Laboratory of Molecular Imaging Probes, Department of Radiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
authors.forename: Mohammed S
authors.initials: MS
authors.lastname: Shazeeb
authors.forename: Yang
authors.initials: Y
authors.lastname: Xie
authors.forename: Suresh
authors.initials: S
authors.lastname: Gupta
authors.forename: Alexei A
authors.initials: AA
authors.lastname: Bogdanov
mesh_terms: D006916:5-Hydroxytryptophan / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D002614:Chelating Agents / Q000737:chemistry / Q000493:pharmacokinetics; D003287:Contrast Media / Q000737:chemistry* / Q000493:pharmacokinetics; D056831:Coordination Complexes / Q000737:chemistry* / Q000493:pharmacokinetics; D004355:Drug Stability; D005260:Female; D005682:Gadolinium / Q000737:chemistry / Q000493:pharmacokinetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D051379:Mice; D008811:Mice, Inbred DBA; D018482:Muscle, Skeletal / Q000378:metabolism; D010084:Oxidation-Reduction; D004369:Pentetic Acid / Q000737:chemistry / Q000493:pharmacokinetics; D009195:Peroxidase / Q000032:analysis / Q000378:metabolism*; D012995:Solubility
chemical_list: D001798:Blood Proteins; D002614:Chelating Agents; D003287:Contrast Media; D056831:Coordination Complexes; D004369:Pentetic Acid; D005682:Gadolinium; D006916:5-Hydroxytryptophan; D009195:Peroxidase