1H NMR and hyperpolarized 13C NMR assays of pyruvate–lactate: a comparative study

Pyruvate–lactate exchange is mediated by the enzyme lactate dehydrogenase (LDH) and is central to the altered energy metabolism in cancer cells. The measurement of exchange kinetics using hyperpolarized ¹³C NMR has provided a biomarker of response to novel therapeutics. However, the observable signal is restricted to the exchanging hyperpolarized ¹³C pools and the endogenous pools of ¹²C‐labelled metabolites are invisible in these measurements. In this study, we investigated an alternative in vitro ¹H NMR assay, using [3‐¹³C]pyruvate, and compared the measured kinetics with a hyperpolarized ¹³C NMR assay, using [1‐¹³C]pyruvate, under the same conditions in human colorectal carcinoma SW1222 cells. The apparent forward reaction rate constants (k_PL) derived from the two assays showed no significant difference, and both assays had similar reproducibility (k_PL = 0.506 ± 0.054 and k_PL = 0.441 ± 0.090 nmol/s/10⁶ cells; mean ± standard deviation; n = 3); ¹H, ¹³C assays, respectively). The apparent backward reaction rate constant (k_LP) could only be measured with good reproducibility using the ¹H NMR assay (k_LP = 0.376 ± 0.091 nmol/s/10⁶ cells; mean ± standard deviation; n = 3). The ¹H NMR assay has adequate sensitivity to measure real‐time pyruvate–lactate exchange kinetics in vitro, offering a complementary and accessible assay of apparent LDH activity. Copyright © 2013 John Wiley & Sons, Ltd.