Stable-isotope-resolved metabolomics revealed that succinate accumulation in cardiac ischemia primarily originates from canonical Krebs cycle activity rather than complex II reversal.
This study clarifies that ischemic succinate accumulation primarily occurs via canonical Krebs cycle activity, highlighting a bifunctional role where accumulation is beneficial during ischemia but oxidation is detrimental during reperfusion.
Succinate accumulates during ischemia, and its oxidation at reperfusion drives injury. The mechanism of ischemic succinate accumulation is controversial and is proposed to involve reversal of mitochondrial complex II. Herein, using stable-isotope-resolved metabolomics, we demonstrate that complex II reversal is possible in hypoxic mitochondria but is not the primary succinate source in hypoxic cardiomyocytes or ischemic hearts. Rather, in these intact systems succinate primarily originates from canonical Krebs cycle activity, partly supported by aminotransferase anaplerosis and glycolysis from glycogen. Augmentation of canonical Krebs cycle activity with dimethyl-α-ketoglutarate both increases ischemic succinate accumulation and drives substrate-level phosphorylation by succinyl-CoA synthetase, improving ischemic energetics. Although two-thirds of ischemic succinate accumulation is extracellular, the remaining one-third is metabolized during early reperfusion, wherein acute complex II inhibition is protective. These results highlight a bifunctional role for succinate: its complex-II-independent accumulation being beneficial in ischemia and its complex-II-dependent oxidation being detrimental at reperfusion.
Zhang et al. (2018) studied Cardiac ischemia. Dimethyl-α-ketoglutarate was evaluated on Mechanism of ischemic succinate accumulation. Stable-isotope-resolved metabolomics revealed that succinate accumulation in cardiac ischemia primarily originates from canonical Krebs cycle activity rather than complex II reversal.