Distinct effects of intracellular vs. extracellular acidic pH on the cardiac metabolome during ischemia and reperfusion

Reactive Oxygen Species Generation by Reverse Electron Transfer at Mitochondrial Complex I Under Simulated Early Reperfusion Conditions

“…Overall, our findings ( Figure 6B ) suggest that Cx-I RET ROS may be less important for the pathology of IR injury than previously thought, while the Cx-III Q site 62 and other ROS generating sites upstream of the Cx-I Q site (e.g., PDH and/or Cx-I flavin) may be more important than currently acknowledged. There are, of course, additional factors that could contribute to the mechanisms of ROS generation in the respiratory chain, including metabolites that accumulate in hypoxia such as L-2-HG, and defects in other metabolic pathways such as glycolysis or the pentose phosphate pathway 26,63 . Nevertheless, in its current state our model of early-reperfusion-like conditions represents a baseline for future studies on this important pathologic phenomenon.…”

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

“…Although fluorescent ATP/ADP biosensors are available [ 49 ], even newer variants achieve maximal signal at ATP/ADP ratios of 10-fold [ 50 ], far below those seen in the heart. Work from ours and other labs suggests that ATP/ADP drops by up to 4-fold during ischemia [ 31 , 45 , 51 ]. As such, we chose three different ATP/ADP ratios to study: 3000/1, representing excess ATP and mimicking state-4 respiration, 145/1 as an intermediate state approximating the normal heart, and 60/1 representing an ischemia-like condition, cognoscent of the rapid recovery of ATP synthesis upon tissue reperfusion.…”

“…Recently, lactate has also been shown to impact mitochondrial function independent of its own metabolism [ 26 ]. In addition to lactate itself ( pK a 3.9), glycolysis generates protons from ATP hydrolysis at hexokinase and phosphofructokinase, and along with protons from CO 2 generated by the TCA cycle [ [27] , [28] , [29] ] this results in intracellular acidification to approximately pH 6.8 in the case of cardiac ischemia [ 30 , 31 ]. We previously reported that acidic pH may stimulate Cx-I RET ROS, but it simultaneously inhibits Cx-II activity, such that it may have no overall effect on succinate-driven Cx-I RET ROS [ 32 ].…”

Influence of acidic metabolic environment on differentiation of stem cell-derived cardiomyocytes

“…Ischemia leads to tissue hypoxia, resulting in acidosis from anaerobic glycolysis of cells; in contrast, reperfusion reoxygenates the myocardial infarcted zone and promotes the recovery of physiological pH ( 17 ). Although acidosis is often considered detrimental to cell survival, numerous studies have shown that acidosis protects against ischemic and hypoxic injury in cardiomyocytes, hepatocytes, and other cells; conversely, reperfusion following prolonged ischemia may cause cell death, an incongruity known as the “pH paradox” ( 18 , 19 ).…”