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Effect of hydrogen peroxide on intracellular pH in the human atrial myocardium
Chao-Ming Chao1, Jong-Shiaw Jin, Chien-Sung Tsai
1Department of Dermatology, National Defense Medical Center, Taipei, Taiwan, Republic of China.
Insights
Hydrogen peroxide (H2O2) causes dose-dependent intracellular acidosis in human atrial tissue, likely via hydroxyl radical (*OH) generation. N-(mercaptopropionyl)-glycine (N-MPG) protects against this, suggesting *OH involvement in oxidative stress.
Area of Science:
- Cardiovascular Physiology
- Biochemistry
- Oxidative Stress Research
Background:
- Myocardial ischemia and reperfusion injury involves complex mechanisms, including hydrogen peroxide (H2O2) accumulation and altered intracellular pH (pHi).
- The specific impact of H2O2 on pHi in human atrial myocardium remains incompletely understood.
Purpose of the Study:
- To investigate the effects of H2O2 on pHi in human atrial myocardium.
- To evaluate the cardioprotective potential of scavengers against H2O2-induced pHi changes.
Main Methods:
- Human atrial tissues were obtained from patients undergoing open-heart surgery.
- Ratiometric recordings of pHi were performed using the fluorescent dye BCECF.
- Tissues were superfused with varying concentrations of H2O2, and effects of N-MPG, L-methionine, and Hoe 694 were assessed.
Main Results:
- H2O2 induced a significant, dose-dependent intracellular acidosis in human atrial myocardium.
- N-(mercaptopropionyl)-glycine (N-MPG) significantly blocked H2O2-induced acidosis, while L-methionine did not.
- The Na+/H+ exchanger (NHE) inhibitor Hoe 694 mimicked the acidosis induced by H2O2, and H2O2 effects persisted even with NHE inhibition.
Conclusions:
- H2O2 induces intracellular acidosis in human atrial muscle primarily through hydroxyl radical (*OH) generation.
- The findings suggest H2O2 inhibits acid extruders, including the NHE, contributing to acidosis.
- N-MPG demonstrates potential cardioprotective effects against H2O2-induced oxidative stress in the human atrium.
Abstract:
The cardiac injury observed during myocardial ischemia and reperfusion has been shown to be a consequence of a complex mechanism in which the accumulation of hydrogen peroxide (H2O2) and other oxygen free radicals (OFRs), and intracellular pH (pHi) are believed to play a major role. However, the effect of H2O2 on pHi has not been well characterized in the human atrial myocardium. In the present study, we superfused hydrogen peroxide into the human atrial tissue in order to assess the effects of oxygen free radicals on the pHi, and, furthermore, to test the ability of certain potential cardioprotective agents, including scavengers of the *OH free radical (N-(mercaptopropionyl)-glycine; N-MPG) and the HOCl free radical (L-methionine), to protect against oxidative-induced pHi challenge. The human atrial tissues were obtained from patients undergoing corrective open-heart surgery. The ratiometric recordings of pHi were measured using the pH-sensitive, dual-excitation and dual-emission fluorescent dye BCECF (2', 7'-bis(carboxyethyl)-5, 6-carboxyfluorescein acetoxymethyl ester). By continuously monitoring pHi changes in human atrial myocardium, we have found, for the first time, that (a) H2O2 (30 microM-3 mM) induced a significant dose-dependent intracellular acidosis, (b) N-MPG caused a significant block on the intracellular acidosis induced by 3 mM H2O2, whereas L-methionine did not, and (c) Hoe 694, a specific Na+/H+ exchanger (NHE) inhibitor, caused a similar extents like that induced by 3 mM H2O2. Our data suggest that the effects of H2O2 are caused mainly through the generation of *OH, which is attributed to the intracellular acidosis seen in the human atrial trabecular muscle. The possible underlying mechanism for H2O2-induced acidosis is likely due to its inhibition on the activity of NHE and other acid extruders, as the pHi changes after H2O2 exposure could be detected even though the activity of NHE was completely blocked by 30 mM Hoe 694.