title: Magnetic susceptibility to measure total protein concentration from NMR metabolite spectra: Demonstration on blood plasma.
abstract: OBJECTIVE
  Accurate metabolite and protein quantification in blood plasma and other body fluids from one single NMR measurement, allowing for improved quantitative metabolic profiling and better assessment of metabolite-protein interactions.
  
  
  METHODS
  The total protein concentration is derived from the common chemical-shift changes-caused by protein-induced bulk magnetic susceptibility (BMS)-measured on well-accessible and exchange-free metabolite resonances. These BMS shifts are simply obtained by external referencing with respect to 3-(trimethylsilyl)propionic-2,2,3,3-d4 acid, sodium salt in a coaxial insert.
  
  
  RESULTS
  Based on blood-plasma data from five volunteers, the estimated accuracy of the BMS method is ≤ 5% with respect and comparable to the 3.8% error of the standard colorimetric, Biuret, method. Valine, alanine, glucose, leucine, and lactate display no exchange-induced shift changes. Their well-accessible signals act as reliable probes for pure protein-induced BMS. The slopes and intercepts of their chemical-shift change versus protein concentration were derived from metabolite mixtures with (fatted) human and bovine albumin acting as blood-plasma mimics.
  
  
  CONCLUSIONS
  The BMS method, demonstrated on blood plasma, can also be used on other samples containing sufficient protein (> 10 g/L). Also, it allows measurement of the presence and sign of exchange-induced chemical-shift changes.
authors.affiliation: Biophysical Chemistry, Institute for Materials and Molecules, Radboud University, Nijmegen, The Netherlands.
authors.forename: Marc
authors.initials: M
authors.lastname: Jupin
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Michiels
authors.forename: Frederic C
authors.initials: FC
authors.lastname: Girard
authors.forename: Sybren S
authors.initials: SS
authors.lastname: Wijmenga
mesh_terms: D000465:Algorithms; D001774:Blood Chemical Analysis / Q000379:methods*; D001798:Blood Proteins / Q000378:metabolism*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D055442:Metabolome / Q000502:physiology; D020543:Proteome / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D001798:Blood Proteins; D020543:Proteome
keywords: NMR; blood plasma; bulk magnetic susceptibility; metabolomics; protein quantification