Effect of potential-dependent potassium uptake on production of reactive oxygen species in rat brain mitochondria

Diazoxide affects mitochondrial bioenergetics by the opening of mKATP channel on submicromolar scale

Background

Cytoprotection afforded by mitochondrial ATP-sensitive K⁺-channel (mK_ATP-channel) opener diazoxide (DZ) largely depends on the activation of potassium cycle with eventual modulation of mitochondrial functions and ROS production. However, generally these effects were studied in the presence of Mg∙ATP known to block K⁺ transport. Thus, the purpose of our work was the estimation of DZ effects on K⁺ transport, K⁺ cycle and ROS production in rat liver mitochondria in the absence of Mg∙ATP.

Results

Without Mg·ATP, full activation of native mK_ATP-channel, accompanied by the increase in ATP-insensitive K⁺ uptake, activation of K⁺-cycle and respiratory uncoupling, was reached at ≤0.5 μM of DZ,. Higher diazoxide concentrations augmented ATP-insensitive K⁺ uptake, but not mK_ATP-channel activity. mK_ATP-channel was blocked by Mg·ATP, reactivated by DZ, and repeatedly blocked by mK_ATP-channel blockers glibenclamide and 5-hydroxydecanoate, whereas ATP-insensitive potassium transport was blocked by Mg²⁺ and was not restored by DZ. High sensitivity of potassium transport to DZ in native mitochondria resulted in suppression of mitochondrial ROS production caused by the activation of K⁺-cycle on sub-micromolar scale. Based on the oxygen consumption study, the share of mK_ATP-channel in respiratory uncoupling by DZ was found.

Conclusions

The study of mK_ATP-channel activation by diazoxide in the absence of MgATP discloses novel, not described earlier, aspects of mK_ATP-channel interaction with this drug. High sensitivity of mK_ATP-channel to DZ results in the modulation of mitochondrial functions and ROS production by DZ on sub-micromolar concentration scale. Our experiments led us to the hypothesis that under the conditions marked by ATP deficiency affinity of mK_ATP-channel to DZ can increase, which might contribute to the high effectiveness of this drug in cardio- and neuroprotection.

Direct Pharmacological Targeting of a Mitochondrial Ion Channel Selectively Kills Tumor Cells In Vivo

The potassium channel Kv1.3 is highly expressed in the mitochondria of various cancerous cells. Here we show that direct inhibition of Kv1.3 using two mitochondria-targeted inhibitors alters mitochondrial function and leads to reactive oxygen species (ROS)-mediated death of even chemoresistant cells independently of p53 status. These inhibitors killed 98% of ex vivo primary chronic B-lymphocytic leukemia tumor cells while sparing healthy B cells. In orthotopic mouse models of melanoma and pancreatic ductal adenocarcinoma, the compounds reduced tumor size by more than 90% and 60%, respectively, while sparing immune and cardiac functions. Our work provides direct evidence that specific pharmacological targeting of a mitochondrial potassium channel can lead to ROS-mediated selective apoptosis of cancer cells in vivo, without causing significant side effects.

Mitochondrial ATP-sensitive potassium channel opening inhibits isoproterenol-induced cardiac hypertrophy by preventing oxidative damage

Cardiac hypertrophy is a chronic complex disease that occurs in response to hemodynamic load and is accompanied by oxidative stress and mitochondrial dysfunction. Mitochondrial ATP-sensitive K channels (mitoKATPs) have previously been shown to prevent oxidative cardiac damage under conditions of ischemia/reperfusion. However, the effect of these channels on cardiac hypertrophy has not been tested to date. In this study, we show that treatment of Swiss mice with isoproterenol (30 mg·kg·d) induces cardiac hypertrophy while significantly decreasing the levels of reduced protein thiols, glutathione, catalase, and superoxide dismutase activity, indicative of a condition of oxidative imbalance. Treatment with diazoxide (a mitoKATP opener, 5 mg·kg·d) normalized the levels of protein thiols and reduced glutathione, rescued superoxide dismutase activity, and significantly prevented cardiac hypertrophy. The protective effects of diazoxide were mitigated by the mitoKATP blockers 5-hydroxydecanoate (5 mg·kg·d) and glibenclamide (3 mg·kg·d), demonstrating that they were related to activation of the channel. Taken together, our results establish that mitoKATP activation promotes very robust prevention of cardiac hypertrophy and associated oxidative imbalance and suggest that these channels can be important drug targets for the pharmacological control of cardiac hypertrophy.

rAAV/ABAD-DP-6His attenuates oxidative stress-induced injury of PC12 cells

Our previous studies have revealed that amyloid β (Aβ)-binding alcohol dehydrogenase (ABAD) decoy peptide antagonizes Aβ42-induced neurotoxicity. However, whether it improves oxidative stress injury remains unclear. In this study, a recombinant adenovirus constitutively secreting and expressing Aβ-ABAD decoy peptide (rAAV/ABAD-DP-6His) was successfully constructed. Our results showed that rAAV/ABAD-DP-6His increased superoxide dismutase activity in hydrogen peroxide-induced oxidative stress-mediated injury of PC12 cells. Moreover, rAAV/ABAD-DP-6His decreased malondialdehyde content, intracellular Ca(2+) concentration, and the level of reactive oxygen species. rAAV/ABAD-DP-6His maintained the stability of the mitochondrial membrane potential. In addition, the ATP level remained constant, and apoptosis was reduced. Overall, the results indicate that rAAV/ABAD-DP-6His generates the fusion peptide, Aβ-ABAD decoy peptide, which effectively protects PC12 cells from oxidative stress injury induced by hydrogen peroxide, thus exerting neuroprotective effects.