title: Differentiating inflamed and normal lungs by the apparent reaction rate constants of lactate dehydrogenase probed by hyperpolarized (13)C labeled pyruvate.
abstract: BACKGROUND
  Clinically translatable hyperpolarized (HP) (13)C-NMR can probe in vivo enzymatic reactions, e.g., lactate dehydrogenase (LDH)-catalyzed reaction by injecting HP (13)C-pyruvate into the subject, which is converted to (13)C labeled lactate by the enzyme. Parameters such as (13)C-lactate signals and lactate-to-pyruvate signal ratio are commonly used for analyzing the HP (13)C-NMR data. However, the biochemical/biological meaning of these parameters remains either unclear or dependent on experimental settings. It is preferable to quantify the reaction rate constants with a clearer physical meaning. Here we report the extraction of the kinetic parameters of the LDH reaction from HP (13)C-NMR data and investigate if they can be potential predictors of lung inflammation.
  
  
  METHODS
  Male Sprague-Dawley rats (12 controls, 14 treated) were used. One dose of bleomycin (2.5 U/kg) was administered intratracheally to the treatment group. The lungs were removed, perfused, and observed by the HP-NMR technique, where a HyperSense dynamic nuclear polarization system was used to generate the HP (13)C-pyruvate for injecting into the lungs. A 20 mm (1)H/(13)C dual-tuned coil in a 9.4-T Varian vertical bore NMR spectrometer was employed to acquire the (13)C spectral data every 1 s over a time period of 300 s using a non-selective, 15-degree radiofrequency pulse. The apparent rate constants of the LDH reaction and their ratio were quantified by applying ratiometric fitting analysis to the time series data of (13)C labeled pyruvate and lactate.
  
  
  RESULTS
  The apparent forward rate constant kp =(3.67±3.31)×10(-4) s(-1), reverse rate constant kl =(4.95±2.90)×10(-2) s(-1), rate constant ratio kp /kl =(7.53±5.75)×10(-3) for the control lungs; kp =(11.71±4.35)×10(-4) s(-1), kl =(9.89±3.89)×10(-2) s(-1), and kp /kl =(12.39±4.18)×10(-3) for the inflamed lungs at the 7(th) day post treatment. Wilcoxon rank-sum test showed that the medians of these kinetic parameters of the 7-day cohort were significantly larger than those of the control cohort (P<0.001, P=0.001, and P=0.019, respectively). The rate constants of individual lungs correlated significantly with the histology scores of neutrophils and organizing pneumonia foci but not macrophages. Both kp and kp /kl positively correlated with lactate labeling signals. No correlation was found between kl and lactate labeling signals.
  
  
  CONCLUSIONS
  The results indicate bleomycin-induced lung inflammation significantly increased both the forward and reverse reaction rate constants of LDH and their ratio at day-7 after bleomycin treatment.
authors.affiliation: 1 Department of Radiology, 2 Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA ; 3 Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: He N
authors.initials: HN
authors.lastname: Xu
authors.affiliation: 1 Department of Radiology, 2 Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA ; 3 Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Kadlececk
authors.affiliation: 1 Department of Radiology, 2 Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA ; 3 Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Hoora
authors.initials: H
authors.lastname: Shaghaghi
authors.affiliation: 1 Department of Radiology, 2 Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA ; 3 Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Huaqing
authors.initials: H
authors.lastname: Zhao
authors.affiliation: 1 Department of Radiology, 2 Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA ; 3 Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Harilla
authors.initials: H
authors.lastname: Profka
authors.affiliation: 1 Department of Radiology, 2 Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA ; 3 Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Pourfathi
authors.affiliation: 1 Department of Radiology, 2 Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA ; 3 Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Rahim
authors.initials: R
authors.lastname: Rizi
authors.affiliation: 1 Department of Radiology, 2 Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA ; 3 Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Lin Z
authors.initials: LZ
authors.lastname: Li
keywords: 13C-pyruvate and lactate; Hyperpolarization; NMR spectroscopy; lactate dehydrogenase (LDH) reaction; lung inflammation