Quantitative assessment of anaplerosis from propionate in pig heart in vivo

Abstract

Normal cardiac metabolism requires continuous replenishment (anaplerosis) of catalytic intermediates of the citric acid cycle. Little is known about the quantitative aspects of propionate as a substrate of in vivo anaplerosis; therefore, we measured the rate of propionate entry into the citric acid cycle in hearts of anesthetized pigs. [U-13C3]propionate (0.25 mM) was infused in a coronary artery branch for 1 h via an extracorporeal perfusion circuit, and cardiac biopsies were analyzed for the mass isotopomer distribution of citric acid cycle intermediates. Infusion of propionate did not affect myocardial oxygen consumption, heart rate, or contractile function. In the infused territory, propionate infusion did not affect uptake of glucose and lactate but decreased free fatty acid uptake by one-half ( P < 0.05). Propionate extraction and uptake were 57.4 ± 3.3% and 0.078 ± 0.009 μmol · min−1 · g−1. Anaplerosis from propionate, calculated from the mass isotopomer distribution of succinate, accounted for 8.9 ± 1.3% of the citric acid cycle flux. Propioylcarnitine release accounted for only 0.033 ± 0.002% of propionate uptake. Methylcitrate did not accumulate. Thus administration of a low concentration of propionate appears to be a convenient and safe way to boost anaplerosis in the heart.

Assessing the Reversibility of the Anaplerotic Reactions of the Propionyl-CoA Pathway in Heart and Liver

“…NaH 13 CO 3 , [U- 13 Perfusions with NaH 13 CO 3 -First, we followed the time course of the labeling of liver methylmalonyl-CoA and succinylCoA from bicarbonate. Fig.…”

“…For this purpose, we perfused livers and hearts with NaH 13 CO 3 , [U- 13 The rapid labeling of methylmalonyl-CoA and succinyl-CoA from 40% enriched bicarbonate reflected a rapid turnover of the intermediates (Fig. 2, A and B).…”

“…The fractional contribution of succinyl-CoA to methylmalonylCoA via the reversal of the methylmalonyl-CoA mutase reaction (FC Succ-CoA 3 MMA-CoA) can be calculated from the M2 enrichments of methylmalonyl-CoA and succinyl-CoA labeled from [U- 13 …”

“…As part of a study on the regulation of anaplerosis from propionyl-CoA precursors in rat livers and hearts, we investigated the degree of reversibility of the reactions of the propionyl-CoA pathway. Label was introduced into the pathway via NaH 13 CO 3 , [U- 13 Adequate energy production via the citric acid cycle (CAC) 1 requires not only a constant supply of acetyl-CoA, but also a fairly constant pool of the catalytic intermediates which carry the acetyl groups as they are oxidized. Although the process of anaplerosis in micro-organisms was discovered in the 1960s (1), its importance for the homeostasis of mammalian cells (particularly cardiomyocytes) was recognized only in the 1980s (2, 3) (for a recent review, see Ref.…”

“…In a follow-up investigation in pig hearts, propionate infusion was found to be a very effective anaplerotic substrate. Anaplerosis from 0.25 mM [U- 13 C 3 ]propionate amounted to 9% of the rate of the CAC (12,13). This led us to investigate the regulation of the propionyl-CoA pathway in livers and hearts of animals.…”