One-pot enzymatic synthesis of l-[3-11C]lactate for pharmacokinetic analysis of lactate metabolism in rat brain

Takashi Temma; Hidekazu Kawashima; Naoya Kondo; Makoto Yamazaki; Kazuhiro Koshino; Hidehiro Iida

doi:10.1016/j.nucmedbio.2018.07.001

One-pot enzymatic synthesis of l-[3-¹¹C]lactate for pharmacokinetic analysis of lactate metabolism in rat brain

Nucl Med Biol. 2018 Sep-Oct:64-65:28-33. doi: 10.1016/j.nucmedbio.2018.07.001. Epub 2018 Jul 7.

Authors

Takashi Temma¹, Hidekazu Kawashima², Naoya Kondo³, Makoto Yamazaki⁴, Kazuhiro Koshino⁵, Hidehiro Iida⁵

Affiliations

¹ Department of Investigative Radiology, National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan; Department of Biofunctional Analysis, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan. Electronic address: ttemma@gly.oups.ac.jp.
² Department of Investigative Radiology, National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan; Radioisotope Research Center, Kyoto Pharmaceutical University, 1 Misasagi-Shichono-cho, Yamashina-ku, Kyoto 607-8412, Japan.
³ Department of Investigative Radiology, National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan; Department of Biofunctional Analysis, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan.
⁴ Department of Investigative Radiology, National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan; Department of Medical & General Sciences, Faculty of Health Sciences, Nihon Institute of Medical Science, 1276 Shimogawara, Moroyamamachi, Irumagun, Saitama 350-0435, Japan.
⁵ Department of Investigative Radiology, National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan.

PMID: 30015093
DOI: 10.1016/j.nucmedbio.2018.07.001

Abstract

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-[3-¹¹C]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 [3-¹¹C]alanine obtained from ¹¹C-methylation of a precursor and deprotection was reacted with an enzyme mixture consisting of alanine racemase, d-amino acid oxidase, catalase, and lactate dehydrogenase to yield l-[3-¹¹C]lactate via [3-¹¹C]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-[3-¹¹C]lactate. PET scans were performed on normal and fasted rats administered with l-[3-¹¹C]lactate.

Results: l-[3-¹¹C]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-[3-¹¹C]lactate injection, rapidly decreased to the minimum value within 90 s, and slowly cleared thereafter. HPLC analysis of blood samples revealed the presence of [¹¹C]glucose (78.9%) and l-[3-¹¹C]lactate (12.1%) 10 min after administration of l-[3-¹¹C]lactate. Insulin pretreatment partly inhibited glyconeogenesis conversion leading to 55.4% as [¹¹C]glucose and 38.9% as l-[3-¹¹C]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-[3-¹¹C]lactate in a one-pot enzymatic synthetic procedure and showed rapid metabolic conversion of l-[3-¹¹C]lactate to [¹¹C]glucose in the blood. PET analysis of l-[3-¹¹C]lactate indicated the possible presence of active lactate usage in rat brains in vivo.

Keywords: Brain; Metabolite; One-pot enzymatic synthesis; PET; Rat; l-[3-(11)C]Lactate.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Brain / diagnostic imaging
Brain / metabolism*
Carbon Radioisotopes*
Chemistry Techniques, Synthetic
Enzymes / metabolism*
Lactic Acid / chemical synthesis*
Lactic Acid / metabolism*
Lactic Acid / pharmacokinetics
Male
Positron-Emission Tomography
Radiochemistry
Rats
Rats, Sprague-Dawley
Tissue Distribution

Substances

Carbon Radioisotopes
Carbon-11
Enzymes
Lactic Acid