title: Amide proton transfer of carnosine in aqueous solution studied in vitro by WEX and CEST experiments.
abstract: Amide protons of peptide bonds induce an important chemical exchange saturation transfer (CEST) contrast in vivo. As a simple in vitro model for a peptide amide proton CEST effect, we suggest herein the dipeptide carnosine. We show that the metabolite carnosine creates a CEST effect and we study the properties of the exchange of the amide proton (-NH) of the carnosine peptide bond (NHCPB) in model solutions for a pH range from 6 to 8.3 and a temperature range from T = 5 °C to 43 °C by means of CEST and water exchange spectroscopy (WEX) experiments on a 3 T whole-body MR tomograph. The dependence of the NHCPB chemical exchange rate k(sw) on pH and temperature T was determined using WEX. For physiological conditions (T = 37 °C, pH = 7.10) we obtained k(sw) = (47.07 ± 7.90)/s. With similar chemical shift and exchange properties to amide protons in vivo, carnosine forms a simple model system for optimization of CEST pulse sequences in vitro. The potential for direct detection of the metabolite carnosine in vivo is discussed.
authors.affiliation: Deutsches Krebsforschungszentrum, German Cancer Research Center (DKFZ), Department of Medical Physics in Radiology, Heidelberg, Germany.
authors.forename: Olga
authors.initials: O
authors.lastname: Bodet
authors.affiliation: Deutsches Krebsforschungszentrum, German Cancer Research Center (DKFZ), Department of Medical Physics in Radiology, Heidelberg, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Goerke
authors.affiliation: Deutsches Krebsforschungszentrum, German Cancer Research Center (DKFZ), Department of Medical Physics in Radiology, Heidelberg, Germany.
authors.forename: Nicolas G R
authors.initials: NG
authors.lastname: Behl
authors.affiliation: Biomedizinische NMR Forschungs GmbH, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.
authors.forename: Volkert
authors.initials: V
authors.lastname: Roeloffs
authors.affiliation: Deutsches Krebsforschungszentrum, German Cancer Research Center (DKFZ), Department of Medical Physics in Radiology, Heidelberg, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Zaiss
authors.affiliation: Deutsches Krebsforschungszentrum, German Cancer Research Center (DKFZ), Department of Medical Physics in Radiology, Heidelberg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Bachert
mesh_terms: D000577:Amides; D002336:Carnosine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011522:Protons; D012996:Solutions; D013696:Temperature
chemical_list: D000577:Amides; D011522:Protons; D012996:Solutions; D002336:Carnosine
keywords: APT; CEST; WEX; carnosine; chemical exchange; pH; peptide bond; proton transfer