A1 Journal article – refereed
One-pot enzymatic synthesis of L-[3-C-11]lactate for pharmacokinetic analysis of lactate metabolism in rat brain

List of Authors: Temma T, Kawashima H, Kondo N, Yamazaki M, Koshino K, Iida H
Publication year: 2018
Journal: Nuclear Medicine and Biology
Journal name in source: NUCLEAR MEDICINE AND BIOLOGY
Journal acronym: NUCL MED BIOL
Volume number: 64-65
Number of pages: 6
ISSN: 0969-8051

Introduction: Lactate could serve as an energy source and signaling molecule in the brain, although there is insufficient in vivo evidence to support this possibility. Here we aimed to use a one-pot enzymatic synthetic procedure to synthesize L-[3-C-11] lactate that can be used to evaluate chemical forms in the blood after intravenous administration, and as a probe for pharmacokinetic analysis of lactate metabolism in in vivo positron emission tomography (PET) scans with normal and fasted rats.Methods: Racemic [3-C-11]alanine obtained from C-11-methylation of a precursor and deprotection was reacted with an enzyme mixture consisting of alanine racemase, n-amino acid oxidase, catalase, and lactate dehydrogenate to yield L-[3-C-11] lactate via [3-C-11]pyruvate. The optical purity was measured by HPLC. Radioactive chemical forms in the arterial blood of Sprague Dawley rats with or without insulin pretreatment were evaluated by HPLC 10 min after bolus intravenous injection of L-[3-C-11]lactate. PET scans were performed on normal and fasted rats administered with L-[3-C-11]lactate.Results: L-[3-C-11]Lactate was synthesized within 50 min and had decay corrected radiochemical yield, radiochemical purity, and optical purity of 13.4%, >95%, and >99%, respectively. The blood radioactivity peaked immediately after L-[3-C-11]lactate injection, rapidly decreased to the minimum value within 90 s, and slowly cleared thereafter. HPLC analysis of blood samples revealed the presence of [C-11]glucose (78.9%) and L-[3-C-11] lactate (12.1%) 10 min after administration of L-[3-C-11]lactate. Insulin pretreatment partly inhibited glyconeogenesis conversion leading to 55.4% as [C-11]glucose and 38.9% as L-[3-C-11]lactate simultaneously. PET analysis showed a higher SUV in the brain tissue of fasted rats relative to non-fasted rats.Conclusions: We successfully synthesized L-[3-C-11]lactate in a one-pot enzymatic synthetic procedure and showed rapid metabolic conversion of L-[3-C-11]lactate to [C-11]glucose in the blood. PET analysis of L-[3-C-11]lactate indicated the possible presence of active lactate usage in rat brains in vivo. (C) 2018 Elsevier Inc. All rights reserved.

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