Mitochondrial Channels and their Role in Cardioprotection

Mitochondria play a pivotal role in cardioprotection. The major cardioprotective mechanism is ischemic preconditioning (IpreC), through which short periods of ischemia protect a subsequent prolonged acute ischemic episode. Mitochondria channels, particularly the potassium channels (mitoK) such as ATP-dependent and calcium-activated potassium channels, have been suggested as trigger or end effectors in IpreC. Activators of mitoK are promising therapeutic agents for the treatment of the myocardial injury due to ischemic episodes. In this chapter, we are summarizing our current knowledge on the physiology function of different mitochondrial channels with a focus on the potassium channels and their mechanism in cardioprotection. Furthermore, the currently under development therapy by targeting the mitochondrial channels for the treatment of heart failure are also discussed.

Influences of remote ischemic preconditioning on postoperative delirium and cognitive dysfunction in adults after cardiac surgery: a meta-analysis of randomized controlled trials

Background Remote ischemic preconditioning (RIPC) has been suggested to confer neuroprotective effect. However, influences of RIPC on postoperative delirium (POD) and cognitive dysfunction (POCD) in adults after cardiac surgery are less known. We performed a meta-analysis of randomized controlled trials (RCTs) to evaluate the effects of RIPC on POD and POCD. Methods Relevant studies were obtained by search of PubMed, Embase, and Cochrane’s Library databases. A random-effect model was used to pool the results. Results Ten RCTs including 2303 adults who received cardiac surgery were included. Pooled results showed that RIPC did not significantly affect the incidence of POD (six RCTs, odds ratio [OR] 1.07, 95% confidence interval [CI] 0.81 to 1.40, P = 0.65) with no significant heterogeneity (I2 = 0%). In addition, combined results showed that RIPC did not significantly reduce the incidence of POCD either (six RCTs, OR 0.64, 95% CI 0.37 to 1.11, P = 0.11) with moderate heterogeneity (I2 = 44%). Sensitivity analysis by excluding one RCT at a time showed consistent results (P values all > 0.05). Conclusions Current evidence from RCTs did not support that RIPC could prevent the incidence of POD or POCD in adults after cardiac surgery. Although these findings may be validated in large-scale RCTs, particularly for the results of POCD, based on these findings, RIPC should not be routinely used as a preventative measure for POD and POCD in adult patients after cardiac surgery.

GATA3 (GATA-Binding Protein 3)/KMT2A (Lysine-Methyltransferase-2A) Complex by Increasing H3K4-3me (Trimethylated Lysine-4 of Histone-3) Upregulates NCX3 (Na + -Ca 2+ Exchanger 3) Transcription and Contributes to Ischemic Preconditioning Neuroprotection

Background and Purpose: NCX3 (Na + -Ca 2+ exchanger 3) plays a relevant role in stroke; indeed its pharmacological blockade or its genetic ablation exacerbates brain ischemic damage, whereas its upregulation takes part in the neuroprotection elicited by ischemic preconditioning. To identify an effective strategy to induce an overexpression of NCX3, we examined transcription factors and epigenetic mechanisms potentially involved in NCX3 gene regulation. Methods: Brain ischemia and ischemic preconditioning were induced in vitro by exposure of cortical neurons to oxygen and glucose deprivation plus reoxygenation (OGD/Reoxy) and in vivo by transient middle cerebral artery occlusion. Western blot and quantitative real-time polymerase chain reaction were used to evaluate transcripts and proteins of GATA3 (GATA-binding protein 3), KMT2A (lysine-methyltransferase-2A), and NCX3. GATA3 and KMT2A binding on NCX3 gene was evaluated by chromatin immunoprecipitation and Rechromatin immunoprecipitation experiments. Results: Among the putative transcription factors sharing a consensus sequence on the ncx3 brain promoter region, GATA3 was the only able to up-regulate ncx3. Interestingly, GATA3 physically interacted with KMT2A, and their overexpression or knocking-down increased or downregulated NCX3 mRNA and protein, respectively. Notably, site-direct mutagenesis of GATA site on ncx3 brain promoter region counteracted GATA3 and KMT2A binding on NCX3 gene. More importantly, we found that in the perischemic cortical regions of preconditioned rats GATA3 recruited KMT2A and the complex H3K4-3me (trimethylated lysine-4 of histone-3) on ncx3 brain promoter region, thus reducing transient middle cerebral artery occlusion–induced damage. Consistently, in vivo silencing of either GATA3 or KMT2A prevented NCX3 upregulation and consequently the neuroprotective effect of preconditioning stimulus. The involvement of GATA3/KMT2A complex in neuroprotection elicited by ischemic preconditioning was further confirmed by in vitro experiments in which the knocking-down of GATA3 and KMT2A reverted the neuroprotection induced by NCX3 overexpression in cortical neurons exposed to anoxic preconditioning followed by oxygen and glucose deprivation plus reoxygenation. Conclusions: Collectively, our results revealed that GATA3/KMT2A complex epigenetically activates NCX3 gene transcription during ischemic preconditioning.

Glutathione S-Transferase and Clusterin, New Players in the Ischemic Preconditioning Renal Protection in a Murine Model of Ischemia and Reperfusion

BACKGROUND/AIMS: Renal ischemia and reperfusion injury (IRI) involves oxidative stress, disruption of microvasculature due to endothelial cell damage, loss of epithelial cell polarity secondary to cytoskeletal alterations, inflammation, and the subsequent transition into a mesenchymal phenotype. Ischemic preconditioning (IPC) has been proposed as a therapeutic strategy to avoid/ameliorate the IRI. Since previous results showed that IPC could have differential effects in kidney cortex vs. kidney medulla, in the present study we analyzed the effectiveness and molecular mechanisms implicated in IPC in both kidney regions. METHODS: We evaluated 3 experimental groups of BALB/c male mice: control (sham surgery); renal ischemia (30 min) by bilateral occlusion of the renal pedicle and reperfusion (48 hours) (I/R); and renal IPC (two cycles of 5 min of ischemia and 5 min of reperfusion) applied just before I/R. Acute kidney injury was evaluated by glomerular filtration rate (GFR), Neutrophil Gelatinase-Associated Lipocalin (NGAL) blood level, and histologic analysis. Oxidative stress was studied measurement the Glutathione S-Transferase (GST) activity, GSH/GSSG ratio, and lipoperoxidation levels. Inflammatory mediators (IL-1β, IL-6, Foxp3, and IL-10) were quantified by qRT-PCR. The endothelial (PECAM-1), epithelial (AQP-1), mesenchymal (Vimentin, Fascin, and Hsp47), iNOS, clusterin, and Hsp27 expression were evaluated (qRT-PCR and/or Western blot). RESULTS: The IPC protocol prevented the decrease of GFR, reduced the plasma NGAL, and ameliorated morphological damage in the kidney cortex after I/R. The IPC also prevented the downregulation of GST activity, lipoperoxidation and ameliorated the oxidized glutathione. In addition, IPC prevented the upregulation of vimentin, fascin, and Hsp47, which was associated with the prevention of the downregulation of AQP1 after I/R. The protective effect of IPC was associated with the upregulation of Hsp27, Foxp3, and IL-10 expression in the renal cortex. However, the upregulation of iNOS, IL-1β, IL-6, and clusterin by I/R were not modified by IPC. CONCLUSION: IPC conferred better protection in the kidney cortex as compared to the kidney medulla. The protective effect of IPC was associated with amelioration of oxidative stress, tubular damage, and the induction of markers of Treg lymphocytes activity in the cortical region. Further studies are needed to evaluate if lower tubular cell stress/damage after I/R may explain the preferential induction of Treg response in the kidney cortex induced by IPC.

Limb Remote Ischemic Preconditioning Applied During Sevoflurane Anesthesia Does Not Protect the Lungs in Patients Undergoing Adult Heart Valve Surgery

Background: Two consistent overall cell protective preconditioning treatments should provide more protection. We hypothesized that limb remote ischemic preconditioning (RIPC, second preconditioning stimulus) applied during sevoflurane inhalation (first preconditioning stimulus) would provide more protection to the lungs of patients undergoing adult heart valve surgery. Methods: In this randomized, placebo-controlled, double-blind trial, 50 patients were assigned to the RIPC group or the placebo group (1:1). Patients in the RIPC group received three 5-min cycles of 300 mmHg cuff inflation/deflation of the left-side lower limb before aortic cross-clamping. Anesthesia consisted of opioids and propofol for induction and sevoflurane for maintenance. The primary end point was comparison of the postoperative arterial–alveolar oxygen tension ratio (a/A ratio) between groups. Secondary end points included comparisons of pulmonary variables, postoperative morbidity and mortality and regional and systemic inflammatory cytokines between groups. Results: In the RIPC group, the a/A ratio and other pulmonary variables exhibited no significant differences throughout the study period compared with the placebo group. No significant differences in either plasma or bronchoalveolar lavage levels of TNF- α were noted between the groups at 10 min after anesthetic induction and 1 h after cross-clamp release. The percentage of neutrophils at 12 h postoperation was significantly increased in the RIPC group compared with the placebo group (91.34±0.00 vs. 89.42±0.10, P = 0.023). Conclusions: Limb RIPC applied during sevoflurane anesthesia did not provide additional significant pulmonary protection following adult valvular cardiac surgery.