The role of opioid receptor agonists in ischemic preconditioning

Protective mitochondrial fission induced by stress-responsive protein GJA1-20k

The Connexin43 gap junction gene GJA1 has one coding exon, but its mRNA undergoes internal translation to generate N-terminal truncated isoforms of Connexin43 with the predominant isoform being only 20 kDa in size (GJA1-20k). Endogenous GJA1-20k protein is not membrane bound and has been found to increase in response to ischemic stress, localize to mitochondria, and mimic ischemic preconditioning protection in the heart. However, it is not known how GJA1-20k benefits mitochondria to provide this protection. Here, using human cells and mice, we identify that GJA1-20k polymerizes actin around mitochondria which induces focal constriction sites. Mitochondrial fission events occur within about 45 s of GJA1-20k recruitment of actin. Interestingly, GJA1-20k mediated fission is independent of canonical Dynamin-Related Protein 1 (DRP1). We find that GJA1-20k-induced smaller mitochondria have decreased reactive oxygen species (ROS) generation and, in hearts, provide potent protection against ischemia-reperfusion injury. The results indicate that stress responsive internally translated GJA1-20k stabilizes polymerized actin filaments to stimulate non-canonical mitochondrial fission which limits ischemic-reperfusion induced myocardial infarction.

Ischemic Preconditioning Improves Resistance Training Session Performance

da Silva Novaes, J, da Silva Telles, LG, Monteiro, ER, da Silva Araujo, G, Vingren, JL, Silva Panza, P, Reis, VM, Laterza, MC, and Vianna, JM. Ischemic preconditioning improves resistance training session performance. J Strength Cond Res XX(X): 000-000, 2020-The aim of this study was to investigate the acute effect of ischemic preconditioning (IPC) in a resistance exercise (RE) training session on the number of repetitions performed, total volume, and rating of perceived exertion in recreationally trained and normotensive men. Sixteen recreationally trained and normotensive men completed 3 RE sessions in a counterbalanced and randomized order: (a) IPC protocol using 220 mm Hg followed by RE (IPC), (b) IPC cuff control protocol with 20 mm Hg followed by RE (CUFF), and (c) no IPC (control) followed by RE (CON). RE was performed with 3 sets of each exercise (bench press, leg press, lateral pulldown, hack machine squat, shoulder press, and Smith back squat) until concentric muscular failure, at 80% of one repetition maximum, with 90 seconds of rest between sets and 2 minutes of rest between exercises. Ischemic preconditioning and CUFF consisted of 4 cycles of 5 minutes of occlusion/low pressure alternating with 5 minutes of no occlusion (0 mm Hg) using a pneumatic tourniquet applied around the subaxillary region of the upper arm. For each condition, the number of repetitions completed, total volume of work performed, and rating of perceived exertion were determined. No significant difference was found for rating of perceived exertion between any experimental protocol. Ischemic preconditioning significantly (p < 0.05) increased the number of repetitions across exercises. Consequently, total volume performed (sum of total number of repetitions x load for each exercise) was significantly higher in IPC (46,170 kg) compared with CON (34,069 kg) and CUFF (36,590 kg) across all exercises. This work may have important implications for athletic populations because it demonstrates increase in muscle performance outcomes during a single RE session. Therefore, performing IPC before RE could be an important exercise prescription recommendation to increase maximum repetition performance and total volume of work performed and thus potentially increase desired training adaptations (i.e., strength and hypertrophy).

Hyperglycemia-Induced Oxidative Stress Abrogates Remifentanil Preconditioning-Mediated Cardioprotection in Diabetic Rats by Impairing Caveolin-3-Modulated PI3K/Akt and JAK2/STAT3 Signaling

Diabetic hearts are more vulnerable to ischemia/reperfusion (I/R) injury and less responsive to remifentanil preconditioning (RPC), but the underlying mechanisms are incompletely understood. Caveolin-3 (Cav-3), the dominant isoform of cardiomyocyte caveolae, is reduced in diabetic hearts in which oxidative stress is increased. This study determined whether the compromised RPC in diabetes was an independent manifestation of hyperglycemia-induced oxidative stress or linked to impaired Cav-3 expression with associated signaling abnormality. RPC significantly attenuated postischemic infarction, cardiac dysfunction, myocardial apoptosis, and 15-F2t-isoprostane production (a specific marker of oxidative stress), accompanied with increased Cav-3 expression and enhanced Akt and STAT3 activation in control but not in diabetic rats. Pretreatment with the antioxidant N-acetylcysteine (NAC) attenuated hyperglycemia-induced reduction of Cav-3 expression and Akt and STAT3 activation and restored RPC-mediated cardioprotection in diabetes, which was abolished by cardiac-specific knockdown of Cav-3 by AAV9-shRNA-Cav-3, PI3K/Akt inhibitor wortmannin, or JAK2/STAT3 inhibitor AG490, respectively. Similarly, NAC could restore RPC protection from high glucose and hypoxia/reoxygenation-induced injury evidenced by decreased levels of LDH release, 15-F2t-isoprostane, O₂ ^-, and JC-1 monomeric cells, which were reversed by caveolae disrupter methyl-β-cyclodextrin, wortmannin, or AG490 in isolated primary cardiomyocytes or siRNAs of Cav-3, Akt, or STAT3 in H9C2 cells. Either methyl-β-cyclodextrin or Cav-3 knockdown reduced Akt and STAT3 activation. Further, the inhibition of Akt activation by a selective inhibitor or siRNA reduced STAT3 activation and vice versa, but they had no effects on Cav-3 expression. Thus, hyperglycemia-induced oxidative stress abrogates RPC cardioprotection by impairing Cav-3-modulated PI3K/Akt and JAK2/STAT3 signaling. Antioxidant treatment with NAC could restore RPC-induced cardioprotection in diabetes by improving Cav-3-dependent Akt and STAT3 activation and by facilitating the cross talk between PI3K/Akt and JAK2/STAT3 signaling pathways.

Hemichannel-mediated volume regulation contributes to IPC-induced cardiomyocyte protection

Cx43 has been documented to be involved in ischemic preconditioning (IPC). However, the participation of Cx43-formed hemichannels in IPC and the potential underlying mechanisms remain unclear. The present study focused on cardiomyocytes' volume regulation during IPC to investigate the role of hemichannels in the IPC-induced cardioprotection. In the study, mice cardiomyocytes were respectively treated with a hemichannel blocker, octanol or 18a-Glycyrrhizic acid (18a-GA), and a Cx43-silenced lentivirus. They were subsequently cultured in hypotonic solution to simulate ischemic reperfusion (SIR) and systemic ischemic preconditioning (SIP). Cell morphology and volumetric (area) change were detected by inverted microscopy at 30 min following the addition of hypotonic solution. Cardiomyocyte mortality was assessed by trypan blue stain assay. The analyses revealed that regardless of the treatments, hypotonic solution aggravated cell edema: Compared with the initial condition (the moment before the solution addition, 0 min), the volumetric area increased significantly 30 min later (for hypotonic+DMSO, 5,050±1,511 vs. 3,464±723 µm²; for hypotonic+scramble lentiviral vector, 5,517±1,128 vs. 2,331±536 µm²; P<0.05, respectively). Either treatment alleviated the edematous condition when a comparison was made between 30 min after the hypotonic addition and 0 min (for hypotonic+octanol, 2,990±765 vs. 2,821±773 µm²; for hypotonic+18a-GA, 4,817±1,306 vs. 4,762±1,271 µm²; for hypotonic+Cx43-silenced, 3,627±688 vs. 3,419±814 µm²; P>0.05 for all). Notably, results indicated that the SIP group had lower mortality rates compared with its SIR counterpart; the hypotonic+octanol, hypotonic+18a-GA, and hypotonic+Cx43-silenced group showed markedly-declined mortality when compared with their respective control groups (respectively, 35.70±1.02, 30.76±2.20 vs. 53.58±2.14%; 30.89±2.37 vs. 54.12±2.55%; P<0.05 for all). The results suggest that ischemic preconditioning may provide cardioprotection by blocking the opening of the hemichannels and further mediating the volume regulation of cardiomyocytes.

Effects of ischemic preconditioning on short-duration cycling performance

It has been demonstrated that ischemic preconditioning (IPC) improves endurance performance. However, the potential benefits during anaerobic events and the mechanism(s) underlying these benefits remain unclear. Fifteen recreational cyclists were assessed to evaluate the effects of IPC of the upper thighs on anaerobic performance, skeletal muscle activation, and metabolic responses during a 60-s sprint performance. After an incremental test and a familiarization visit, subjects were randomly submitted in visits 3 and 4 to a performance protocol preceded by intermittent bilateral cuff inflation (4 × (5 min of blood flow restriction + 5 min reperfusion)) at either 220 mm Hg (IPC) or 20 mm Hg (control). To increase data reliability, each intervention was replicated, which was also in a random manner. In addition to the mean power output, the pulmonary oxygen uptake, blood lactate kinetics, and quadriceps electromyograms (EMGs) were analyzed during performance and throughout 45 min of passive recovery. After IPC, performance was improved by 2.1% compared with control (95% confidence intervals of 0.8% to 3.3%, P = 0.001), followed by increases in (i) the accumulated oxygen deficit, (ii) the amplitude of blood lactate kinetics, (iii) the total amount of oxygen consumed during recovery, and (iv) the overall EMG amplitude (P < 0.05). In addition, the ratio between EMG and power output was higher during the final third of performance after IPC (P < 0.05). These results suggest an increased skeletal muscle activation and a higher anaerobic contribution as the ultimate responses of IPC on short-term exercise performance.

Effects of ischemic preconditioning on maximal constant-load cycling performance

This study investigated the effects of ischemic preconditioning (IPC) on the ratings of perceived exertion (RPE), surface electromyography, and pulmonary oxygen uptake (V̇o2) onset kinetics during cycling until exhaustion at the peak power output attained during an incremental test. A group of 12 recreationally trained cyclists volunteered for this study. After determination of peak power output during an incremental test, they were randomly subjected on different days to a performance protocol preceded by intermittent bilateral cuff pressure inflation to 220 mmHg (IPC) or 20 mmHg (control). To increase data reliability, the performance visits were replicated, also in a random manner. There was an 8.0% improvement in performance after IPC (control: 303 s, IPC 327 s, factor SDs of ×/÷1.13, P = 0.01). This change was followed by a 2.9% increase in peak V̇o2 (control: 3.95 l/min, IPC: 4.06 l/min, factor SDs of ×/÷1.15, P = 0.04), owing to a higher amplitude of the slow component of the V̇o2 kinetics (control: 0.45 l/min, IPC: 0.63 l/min, factor SDs of ×/÷2.21, P = 0.05). There was also an attenuation in the rate of increase in RPE ( P = 0.01) and a progressive increase in the myoelectrical activity of the vastus lateralis muscle ( P = 0.04). Furthermore, the changes in peak V̇o2 ( r = 0.73, P = 0.007) and the amplitude of the slow component ( r = 0.79, P = 0.002) largely correlated with performance improvement. These findings provide a link between improved aerobic metabolism and enhanced severe-intensity cycling performance after IPC. Furthermore, the delayed exhaustion after IPC under lower RPE and higher skeletal muscle activation suggest they have a role on the ergogenic effects of IPC on endurance performance.

Nitrite Confers Preconditioning and Cytoprotection After Ischemia/Reperfusion Injury Through the Modulation of Mitochondrial Function

SIGNIFICANCE

Nitrite is now recognized as an intrinsic signaling molecule that mediates a number of biological processes. One of the most reproducible effects of nitrite is its ability to mediate cytoprotection after ischemia/reperfusion (I/R). This robust phenomenon has been reproduced by a number of investigators in varying animal models focusing on different target organs. Furthermore, nitrite's cytoprotective versatility is highlighted by its ability to mediate delayed preconditioning and remote conditioning in addition to acute protection.

RECENT ADVANCES

In the last 10 years, significant progress has been made in elucidating the mechanisms underlying nitrite-mediated ischemic tolerance.

CRITICAL ISSUES

The mitochondrion, which is essential to both the progression of I/R injury and the protection afforded by preconditioning, has emerged as a major subcellular target for nitrite. This review will outline the role of the mitochondrion in I/R injury and preconditioning, review the accumulated preclinical studies demonstrating nitrite-mediated cytoprotection, and finally focus on the known interactions of nitrite with mitochondria and their role in the mechanism of nitrite-mediated ischemic tolerance.

FUTURE DIRECTIONS

These studies set the stage for current clinical trials testing the efficacy of nitrite to prevent warm and cold I/R injury.

The Role of NMDA Receptors in the Development of Brain Resistance through Pre- and Postconditioning

Brain tolerance or resistance can be achieved by interventions before and after injury through potential toxic agents used in low stimulus or dose. For brain diseases, the neuroprotection paradigm desires an attenuation of the resulting motor, cognitive, emotional, or memory deficits following the insult. Preconditioning is a well-established experimental and clinical translational strategy with great beneficial effects, but limited applications. NMDA receptors have been reported as protagonists in the adjacent cellular mechanisms contributing to the development of brain tolerance. Postconditioning has recently emerged as a new neuroprotective strategy, which has shown interesting results when applied immediately, i.e. several hours to days, after a stroke event. Investigations using chemical postconditioning are still incipient, but nevertheless represent an interesting and promising clinical strategy. In the present review pre- and postconditioning are discussed as neuroprotective paradigms and the focus of our attention lies on the participation of NMDA receptors proteins in the processes related to neuroprotection.

Remote ischemic preconditioning preserves mitochondrial function and activates pro-survival protein kinase Akt in the left ventricle during cardiac surgery: a randomized trial

BACKGROUND

Understanding the intracellular mechanisms induced by remote ischemic preconditioning (RIPC) in the human left ventricle opens new possibilities for development of pharmacological cardioprotection against ischemia and reperfusion injury. In this study we investigated the effects of RIPC on mitochondrial function, activation of pro-survival protein kinase Akt and microRNA expression in left ventricular biopsies from patients undergoing coronary artery bypass surgery (CABG).

METHODS

Sixty patients were randomized to control (n=30) or RIPC (n=30). A blood pressure cuff was applied to the arm of all patients preoperatively. The cuff remained deflated in control group, whereas RIPC was performed by 3 cycles of cuff inflation to 200 mm Hg for 5 min, separated by 5 min deflation intervals. Left ventricular biopsies were obtained before and 15 min after aortic declamping. The primary outcome was mitochondrial respiration measured in situ. Secondary outcomes were activation of protein kinase Akt, assessed by western immunoblotting, and expression of microRNAs assessed by array and real-time polymerase chain reaction.

RESULTS

Mitochondrial respiration was preserved during surgery in patients receiving RIPC (+0.2 μmol O2/min/g, p=0.69), and reduced by 15% in controls (-1.5 μmol O2/min/g, p=0.02). Furthermore, RIPC activated protein kinase Akt before aortic clamping (difference from control +43.3%, p=0.04), followed by increased phosphorylation of Akt substrates at reperfusion (+26.8%, p<0.01). No differences were observed in microRNA expression.

CONCLUSIONS

RIPC preserves mitochondrial function and activates pro-survival protein kinase Akt in left ventricle of patients undergoing CABG. Modulation of mitochondrial function and Akt activation should be further explored as cardioprotective drug targets.

CLINICAL TRIAL REGISTRATION

http://www.clinicaltrials.gov, unique identifier: NCT01308138.

Potential of caveolae in the therapy of cardiovascular and neurological diseases

Caveolae are membrane micro-domains enriched in cholesterol, sphingolipids and caveolins, which are transmembrane proteins with a hairpin-like structure. Caveolae participate in receptor-mediated trafficking of cell surface receptors and receptor-mediated signaling. Furthermore, caveolae participate in clathrin-independent endocytosis of membrane receptors. On the one hand, caveolins are involved in vascular and cardiac dysfunction. Also, neurological abnormalities in caveolin-1 knockout mice and a link between caveolin-1 gene haplotypes and neurodegenerative diseases have been reported. The aim of this article is to present the rationale for considering caveolae as potential targets in cardiovascular and neurological diseases.

Cardioprotective effect of betulinic Acid on myocardial ischemia reperfusion injury in rats

Objectives. This study aims to investigate the effect of betulinic acid (BA) on myocardial ischemia reperfusion/injury in an open-chest anesthetized rat model. Methods. The model was induced by 30 minutes left anterior descending occlusion followed by 2 hours reperfusion. There are six groups in our present study: sham operation group, ischemia/reperfusion group, low-dosage BA group, medium-dosage BA group, high-dosage BA group, and fosinopril sodium group. Rats in the latter four groups were administrated with BA (50, 100, and 200 mg/kg, i.g.) or fosinopril sodium (10 mg/kg, i.g.) once a day for 7 days before operation, respectively. Rats in the former two groups were given the same volume of vehicle (0.5% CMC-Na, i.g.). During the operation, cardiac function was continuously monitored. Serum LDH and CK were measured with colorimetric assays. The expression of Bcl-2 and Bax and the apoptosis of cardiomyocytes were investigated with western blot and TUNEL assay, respectively. Results. Pretreatment with BA improved cardiac function and attenuated LDH and CK activities compared with IR group. Further investigation demonstrated that the expression of Bcl-2 and Bax and TUNEL assay was in line with the above results. Conclusion. BA may reduce the release of LDH and CK, prevent cardiomyocytes apoptosis, and eventually alleviate the extent of the myocardial ischemia/reperfusion injury.

Remote ischemic preconditioning preserves mitochondrial function and influences myocardial microRNA expression in atrial myocardium during coronary bypass surgery

RATIONALE

Remote ischemic preconditioning (RIPC) has been suggested to induce cardioprotection during cardiac surgery. Maintaining proper atrial function is imperative in preventing arrhythmia and thrombus formation. Mitochondria have been proposed as key targets in conveying RIPC mechanisms and effects. MicroRNA (miR) is emerging as an important regulator of mitochondrial function, arrhythmia, and protection from ischemia and reperfusion.

OBJECTIVE

This study aimed to evaluate the effect of RIPC on mitochondrial respiration and miR expression in human atrial tissue.

METHODS AND RESULTS

Sixty patients undergoing coronary artery bypass graft surgery were randomized to RIPC (n=30) or control (n=30). RIPC was performed preoperatively by inflating a blood pressure cuff on the upper arm to 200 mm Hg for 3×5 minutes, with 5 minutes reperfusion intervals. Biopsies were obtained from the right atrial appendage before and after aortic cross-clamping. Mitochondrial respiration was measured in situ and miR assessed by commercial miR array and quantitative reverse transcription polymerase chain reaction. Postoperative atrial fibrillation occurrence was monitored by biotelemetry. Maximal mitochondrial respiration was preserved throughout surgery after RIPC but significantly reduced (-28%; P<0.05) after aortic cross-clamping in control. Incidence of postoperative atrial fibrillation was lower after RIPC versus control (14% versus 50%; P<0.01). Myocardial expression of miR-133a and miR-133b increased after aortic cross-clamping in both RIPC and control, whereas miR-1 was upregulated in control only. MiR-338-3p expression was higher in RIPC versus control after aortic cross-clamping.

CONCLUSIONS

RIPC preserves mitochondrial respiration and prevents upregulation of miR-1 in the right atrium during coronary artery bypass graft.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01308138.