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Diazoxide triggers cardioprotection against apoptosis induced by oxidative stress
Masashi Ichinose1, Hidetoshi Yonemochi, Toshiaki Sato
1Department of Laboratory Medicine, Oita Medical University, Japan.
Abstract:
Although mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels have been reported to reduce the extent of apoptosis, the critical timing of mitoK(ATP) channel opening required to protect myocytes against apoptosis remains unclear. In the present study, we examined whether the mitoK(ATP) channel serves as a trigger of cardioprotection against apoptosis induced by oxidative stress. Apoptosis of cultured neonatal rat cardiomyocytes was determined by flow cytometry (light scatter and propidium iodide/annexin V-FITC fluorescence) and by nuclear staining with Hoechst 33342. Mitochondrial membrane potential (DeltaPsi) was measured by flow cytometry of cells stained with rhodamine-123 (Rh-123). Exposure to H(2)O(2) (500 microM) induced apoptosis, and the percentage of apoptotic cells increased progressively and peaked at 2 h. This H(2)O(2)-induced apoptosis was associated with the loss of DeltaPsi, and the time course of decrease in Rh-123 fluorescence paralleled that of apoptosis. Pretreatment of cardiomyocytes with diazoxide (100 microM), a putative mitoK(ATP) channel opener, for 30 min before exposure to H(2)O(2) elicited transient and mild depolarization of DeltaPsi and consequently suppressed both apoptosis and DeltaPsi loss after 2-h exposure to H(2)O(2). These protective effects of diazoxide were abrogated by the mitoK(ATP) channel blocker 5-hydroxydecanoate (500 microM) but not by the sarcolemmal K(ATP) channel blocker HMR-1098 (30 microM). Our results suggest for the first time that diazoxide-induced opening of mitoK(ATP) channels triggers cardioprotection against apoptosis induced by oxidative stress in rat cardiomyocytes.
Insights
Opening mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels with diazoxide triggers cardioprotection against oxidative stress-induced apoptosis in rat heart cells. This finding clarifies the critical timing for mitoK(ATP) channel opening in myocyte protection.
Area of Science:
- Cardiovascular Biology
- Cellular Physiology
- Mitochondrial Medicine
Background:
- Mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels are implicated in cardioprotection, but their precise role and optimal opening time against apoptosis remain undefined.
- Oxidative stress is a significant contributor to myocyte apoptosis, a key factor in cardiac dysfunction.
Purpose of the Study:
- To investigate if the opening of mitoK(ATP) channels acts as a trigger for cardioprotection against oxidative stress-induced apoptosis.
- To determine the critical timing of mitoK(ATP) channel activation for myocyte survival.
Main Methods:
- Neonatal rat cardiomyocytes were subjected to hydrogen peroxide (H(2)O(2)) to induce oxidative stress and apoptosis.
- Apoptosis was quantified using flow cytometry (propidium iodide/annexin V-FITC) and Hoechst 33342 nuclear staining.
- Mitochondrial membrane potential (DeltaPsi) was assessed via rhodamine-123 fluorescence flow cytometry.
- Cardioprotective effects were evaluated using diazoxide (mitoK(ATP) channel opener) and 5-hydroxydecanoate (mitoK(ATP) channel blocker).
Main Results:
- H(2)O(2) exposure induced progressive apoptosis and loss of DeltaPsi in cardiomyocytes, peaking at 2 hours.
- Pretreatment with diazoxide transiently altered DeltaPsi and significantly suppressed H(2)O(2)-induced apoptosis and DeltaPsi loss.
- The protective effects of diazoxide were abolished by 5-hydroxydecanoate but not by the sarcolemmal K(ATP) channel blocker HMR-1098.
Conclusions:
- Diazoxide-induced opening of mitoK(ATP) channels initiates cardioprotection against apoptosis.
- This study establishes a critical role for timely mitoK(ATP) channel activation in mitigating oxidative stress-related myocyte death.