Middle age aggravates myocardial ischemia through surprising upholding of complex II activity, oxidative stress, and reduced coronary perfusion

Abstract

Aging compromises restoration of the cardiac mechanical function during reperfusion. We hypothesized that this was due to an ampler release of mitochondrial reactive oxygen species (ROS). This study aimed at characterising ex vivo the mitochondrial ROS release during reperfusion in isolated perfused hearts of middle-aged rats. Causes and consequences on myocardial function of the observed changes were then evaluated. The hearts of rats aged 10-or 52-week old were subjected to global ischemia followed by reperfusion. Mechanical function was monitored throughout the entire procedure. Activities of the respiratory chain complexes and the ratio of aconitase to fumarase activities were determined before ischemia and at the end of reperfusion. H 2 O 2 release was also evaluated in isolated mitochondria. During ischemia, middle-aged hearts displayed a delayed contracture, suggesting a maintained ATP production but also an increased metabolic proton production. Restoration of the mechanical function during reperfusion was however reduced in the middle-aged hearts, due to lower recovery of the coronary flow associated with higher mitochondrial oxidative stress indicated by the aconitase to fumarase ratio in the cardiac tissues. Surprisingly, activity of the respiratory chain complex II was better maintained in the hearts of middle-aged animals, probably because of an enhanced preservation of its membrane lipid environment. This can explain the higher mitochondrial oxidative stress observed in these conditions, since cardiac mitochondria produce much more H 2 O 2 when they oxidize FADH 2 -linked substrates than when they use NADH-linked substrates. In conclusion, the lower restoration of the cardiac mechanical activity during reperfusion in the middle-aged hearts was due to an impaired recovery of the coronary flow and an insufficient oxygen supply. The deterioration AGE (2011) of the coronary perfusion was explained by an increased mitochondrial ROS release related to the preservation of complex II activity during reperfusion.

Increased Abdominal Adiposity Exacerbates Ex-Vivo Cardiac Reperfusion Injury through Augmented Mitochondrial Oxidative Stress

“…This was attributed to the surprising maintenance of complex-II activity and increased ROS production [40]. Preliminary results from our laboratory show a huge increase in IAA between 3 and 6 months of age and relative stabilization thereafter [58].…”

“…Protease (subtilisin 0.02%) was added to digest the myofibrils for 1 min at 4°C and the whole preparation was then homogenized with the grinder (at 300 rpm, for 3-4 transitions). Subtilisin action was stopped by adding complex activities were also measured in homogenates from the reperfused myocardium, as previously described [40]. Proteins were measured using the bicinchoninic acid method (Thermo Scientific, Rockford, IL) [45].…”

“…Oxidative phosphorylation and mH 2 O 2 r were determined as previously described [40]. Two different respiration buffers with different calcium concentrations (0 or 10 µM) were used.…”

“…All measurements were performed on mitochondria (0.2 mg mitochondrial protein/mL) incubated with freshly prepared pyruvate (5.5 mM)/malate (2.5 mM) or DLpalmitoylcarnitine (50 µM)/malate (2.5 mM), or a combination of these three substrates. State-III and state-IV respiration rates (StIII and StIV), as well as the respiratory control ratio (RCR), were determined as previously described [40]. The mH 2 O 2 r was determined during state-II respiration.…”

“…Calcium is known to trigger the accumulation of the Krebs-cycle intermediate, succinate, in the mitochondrial environment [56]. Succinate enters the respiratory chain at the level of complex II and induces a huge mH 2 O 2 r at the complex-I level, via a reverse electron flux [40]. Since the activity of complex II was higher in IAA, the mH 2 O 2 r was thus higher.…”