Hyperpolarized [13C]ketobutyrate, a molecular analog of pyruvate with modified specificity for LDH isoforms

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Abstract

Purpose:

The purpose of this study was to investigate 13C hyperpolarization of α-ketobutyrate (αKB), an endogenous molecular analog of pyruvate, and its in vivo enzymatic conversion via lactate dehydrogenase (LDH) using localized MR spectroscopy.

Methods:

Hyperpolarized (HP) 13C MR experiments were conducted using [13C]αKB with rats in vivo and with isolated LDH enzyme in vitro, along with comparative experiments using [13C]pyruvate. Based on differences in the kinetics of its reaction with individual LDH isoforms, HP [13C]αKB was investigated as a novel MR probe, with added specificity for activity of LDHB-expressed H (“heart”-type) subunits of LDH (e.g., constituents of LDH-1 isoform).

Results:

Comparable T1 and polarization values to pyruvate were attained (T1 = 52 s at 3 tesla [T], polarization = 10%, at C1). MR experiments showed rapid enzymatic conversion with substantially increased specificity. Formation of product HP [13C]α-hydroxybutyrate (αHB) from αKB in vivo was increased 2.7-fold in cardiac slabs relative to liver and kidney slabs. In vitro studies resulted in 5.0-fold higher product production from αKB with bovine heart LDH-1, as compared with pyruvate.

Conclusions:

HP [13C]αKB may be a useful MR probe of cardiac metabolism and other applications where the role of H subunits of LDH is significant (e.g., renal cortex and brain). Magn Reson Med 75:1894–1900, 2016. © 2015 Wiley Periodicals, Inc.

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