Hyperpolarized C-13 Magnetic Resonance Spectroscopy Reveals the Rate-Limiting Role of the Blood-Brain Barrier in the Cerebral Uptake and Metabolism of L-Lactate in Vivo

The dynamics of L-lactate transport across the blood-brain barrier (BBB) and its cerebral metabolism are still subject to debate. We studied lactate uptake and intracellular metabolism in the mouse brain using hyperpolarized C-13 magnetic resonance spectroscopy (MRS). Following the intravenous injection of hyperpolarized [1-C-13]lactate, we observed that the distribution of the C-13 label between lactate and pyruvate, which has been shown to be representative of their pool size ratio, is different in NMRI and C57BL/6 mice, the latter exhibiting a higher level of cerebral lactate dehydrogenase A (Ldha) expression. On the basis of this observation, and an additional set of experiments showing that the cerebral conversion of [1-C-13]lactate to [1-C-13]pyruvate increases after exposing the brain to ultrasound irradiation that reversibly opens the BBB, we concluded that lactate transport is rate-limited by the BBB, with a 30% increase in lactate uptake after its disruption. It was also deduced from these results that hyperpolarized C-13 MRS can be used to detect a variation in cerebral lactate uptake of