Reactive oxygen species generation by reverse electron transfer at mitochondrial complex I under simulated early reperfusion conditions

Redox Biol. 2024 Apr:70:103047. doi: 10.1016/j.redox.2024.103047. Epub 2024 Jan 27.


Ischemic tissues accumulate succinate, which is rapidly oxidized upon reperfusion, driving a burst of mitochondrial reactive oxygen species (ROS) generation that triggers cell death. In isolated mitochondria with succinate as the sole metabolic substrate under non-phosphorylating conditions, 90 % of ROS generation is from reverse electron transfer (RET) at the Q site of respiratory complex I (Cx-I). Together, these observations suggest Cx-I RET is the source of pathologic ROS in reperfusion injury. However, numerous factors present in early reperfusion may impact Cx-I RET, including: (i) High [NADH]; (ii) High [lactate]; (iii) Mildly acidic pH; (iv) Defined ATP/ADP ratios; (v) Presence of the nucleosides adenosine and inosine; and (vi) Defined free [Ca2+]. Herein, experiments with mouse cardiac mitochondria revealed that under simulated early reperfusion conditions including these factors, total mitochondrial ROS generation was only 56 ± 17 % of that seen with succinate alone (mean ± 95 % confidence intervals). Of this ROS, only 52 ± 20 % was assignable to Cx-I RET. A further 14 ± 7 % could be assigned to complex III, with the remainder (34 ± 11 %) likely originating from other ROS sources upstream of the Cx-I Q site. Together, these data suggest the relative contribution of Cx-I RET ROS to reperfusion injury may be overestimated, and other ROS sources may contribute a significant fraction of ROS in early reperfusion.

Keywords: Complex-I; Ischemia; Mitochondria; Reactive oxygen species; Reperfusion; Reverse electron transfer.

MeSH terms

  • Animals
  • Electron Transport
  • Electron Transport Complex I* / metabolism
  • Electrons
  • Mice
  • Mitochondria, Heart / metabolism
  • Reactive Oxygen Species / metabolism
  • Reperfusion
  • Reperfusion Injury* / metabolism
  • Succinates


  • Reactive Oxygen Species
  • Electron Transport Complex I
  • Succinates