In vivo 13C saturation transfer effect of the lactate dehydrogenase reaction

Lactate dehydrogenase (LDH, EC 1.1.1.27) catalyzes an exchange reaction between pyruvate and lactate. It is demonstrated here that this reaction is sufficiently fast to cause a significant magnetization (saturation) transfer effect when the C-13 resonance of pyruvate is saturated by a continuous-wave (CW) RF pulse. Infusion of [2- 13C]glucose was used to allow labeling of pyruvate C2 at 207.9 ppm to determine the pseudo first-order rate constant of the unidirectional lactate -> pyruvate flux in vivo. During systemic administration of GABA(A) receptor antagonist bicuculline, this pseudo first-order rate constant was determined to be 0.08 0.01 s-1 (mean SD, N = 4) in halothane-anesthetized adult rat brains. In 9L and C6 rat glioma models, the 13C saturation transfer effect of the LDH reaction was also detected in vivo. Our results demonstrate that the 13C magnetization transfer effect of the LDH reaction may be useful as a novel marker for utilizing noninvasive in vivo MRS to study many physiological and pathological conditions, such as cancer. Magn Reson Med 57:258-264, 2007. (c) 2007 Wiley-Liss, Inc.(+)