Differentiating inflamed and normal lungs by the apparent reaction rate constants of lactate dehydrogenase probed by hyperpolarized13 C labeled pyruvate

Quantitative Imaging in Medicine and Surgery

Lin Z. Li³  Huaqing Zhao¹  Stephen Kadlececk²  Hoora Shaghaghi²  Mehrdad Pourfathi²  He N. Xu³  Harilla Profka²  Rahim Rizi² 

[1]Department of Clinical Sciences, Temple University School of Medicine, Philadelphia, PA 19140, USA

[2]Department of Radiology,Department of Radiology, Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA

关键词: Hyperpolarization;    NMR spectroscopy;    lactate dehydrogenase (LDH) reaction;    13C-pyruvate and lactate;    lung inflammation;   

DOI  :  10.3978/j.issn.2223-4292.2016.02.04

学科分类：外科医学

来源: AME Publications

【 摘 要 】

Background: Clinically translatable hyperpolarized (HP) ¹³C-NMR can probe in vivo enzymatic reactions, e.g., lactate dehydrogenase (LDH)-catalyzed reaction by injecting HP ¹³C-pyruvate into the subject, which is converted to ¹³C labeled lactate by the enzyme. Parameters such as ¹³C-lactate signals and lactate-to-pyruvate signal ratio are commonly used for analyzing the HP ¹³C-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 ¹³C-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 ¹³C-pyruvate for injecting into the lungs. A 20 mm ¹H/¹³C dual-tuned coil in a 9.4-T Varian vertical bore NMR spectrometer was employed to acquire the ¹³C 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 ¹³C labeled pyruvate and lactate.

Results: The apparent forward rate constant k_p=(3.67±3.31)×10^�?4 s^�?1, reverse rate constant k_l=(4.95±2.90)×10^�?2 s^�?1, rate constant ratio k_p/k_l=(7.53±5.75)×10^�?3 for the control lungs; k_p=(11.71±4.35)×10^�?4 s^�?1, k_l=(9.89±3.89)×10^�?2 s^�?1, and k_p/k_l=(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 k_p and k_p/k_l positively correlated with lactate labeling signals. No correlation was found between k_l 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.

【 授权许可】

Unknown