Production of hyperpolarized <sup>13</sup>CO<inf>2</inf> from [1-<sup>13</sup>C]pyruvate in perfused liver does reflect total anaplerosis but is not a reliable biomarker of glucose production

Karlos X. Moreno, Christopher L. Moore, Shawn C. Burgess, A. Dean Sherry, Craig R. Malloy, Matthew E. Merritt

Research output: Contribution to journalArticle

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Abstract

In liver, <sup>13</sup>CO<inf>2</inf> can be generated from [1-<sup>13</sup>C]pyruvate via pyruvate dehydrogenase or anaplerotic entry of pyruvate into the TCA cycle followed by decarboxylation at phosphoenolpyruvate carboxykinase (PEPCK), the malic enzyme, isocitrate dehydrogenase, or α-ketoglutarate dehydrogenase. The purpose of this study was to determine the relative importance of these pathways in production of hyperpolarized (HP) <sup>13</sup>CO<inf>2</inf> after administration of hyperpolarized pyruvate in livers supplied with a fatty acid plus substrates for gluconeogenesis. Isolated mouse livers were perfused with a mixture of thermally-polarized <sup>13</sup>C-enriched pyruvate, lactate and octanoate in various combinations prior to exposure to HP pyruvate. Under all perfusion conditions, HP malate, aspartate and fumarate were detected within ~3 s showing that HP [1-<sup>13</sup>C]pyruvate is rapidly converted to [1-<sup>13</sup>C]oxaloacetate which can subsequently produce HP <sup>13</sup>CO<inf>2</inf> via decarboxylation at PEPCK. Measurements using HP [2-<sup>13</sup>C]pyruvate allowed the exclusion of reactions related to TCA cycle turnover as sources of HP <sup>13</sup>CO<inf>2</inf>. Direct measures of O<inf>2</inf> consumption, ketone production, and glucose production by the intact liver combined with <sup>13</sup>C isotopomer analyses of tissue extracts yielded a comprehensive profile of metabolic flux in perfused liver. Together, these data show that, even though the majority of HP <sup>13</sup>CO<inf>2</inf> derived from HP [1-<sup>13</sup>C]pyruvate in livers exposed to fatty acids reflects decarboxylation of [4-<sup>13</sup>C]oxaloacetate (PEPCK) or [4-<sup>13</sup>C]malate (malic enzyme), the intensity of the HP <sup>13</sup>CO<inf>2</inf> signal is not proportional to glucose production because the amount of pyruvate returned to the TCA cycle via PEPCK and pyruvate kinase is variable, depending upon available substrates.

Original languageEnglish (US)
Pages (from-to)1144-1156
Number of pages13
JournalMetabolomics
Volume11
Issue number5
DOIs
Publication statusPublished - Oct 7 2015

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Keywords

  • Gluconeogenesis
  • Hyperpolarization
  • Hyperpolarized <sup>13</sup>CO<inf>2</inf> production
  • Liver metabolism
  • Pyruvate cycling

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Biochemistry
  • Endocrinology, Diabetes and Metabolism

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