Postconditioning: Current Controversies and Clinical Implications

Involvement of exogenous H2S in recovery of cardioprotection from ischemic post-conditioning via increase of autophagy in the aged hearts

BACKGROUND

Hydrogen sulfide (H2S), which is a member of the gasotransmitter family, plays an important physiological and pathological role in cardiovascular system. Ischemic post-conditioning (PC) provides myocardial protective effect in the young hearts but not in the aged hearts. Exogenous H2S restores PC-induced cardioprotection by inhibition of mitochondrial permeability transition pore (mPTP) in the aged hearts. However, whether H2S contributes to the recovery of PC-induced cardioprotection via up-regulation of autophagy in the aged hearts is unclear.

METHODS

The isolated aged rat hearts (24-months-old, 450-500g) and aged cardiomyocytes-induced by d-galactose were exposed to an ischemia/reperfusion (I/R) and PC protocol.

RESULTS

We found PC lost cardioprotection in the aged hearts and cardiomyocytes. NaHS (a H2S donor) significantly restored cardioprotection of PC through decreasing myocardial damage, infarct size, and apoptosis, improving cardiac function, increasing cell viability and autophagy in the aged hearts and cardiomyocytes. 3-MA (an autophagy inhibitor) abolished beneficial effect of NaHS in the aged hearts. In addition, in the aged cardiomyocytes, NaHS up-regulated AMPK/mTOR pathway, and the effect of NaHS on PC was similar to the overexpression of Atg 5, treatment of AICAR (an AMPK activator) or Rapamycin (a mTOR inhibitor, an autophagy activator), respectively.

CONCLUSIONS

These results suggest that exogenous H2S restores cardioprotection from PC by up-regulation of autophagy via activation of AMPK/mTOR pathway in the aged hearts and cardiomyocytes.

Exogenous hydrogen sulfide restores cardioprotection of ischemic post-conditioning via inhibition of mPTP opening in the aging cardiomyocytes

The physiological and pathological roles of hydrogen sulfide (H₂S) in the regulation of cardiovascular functions have been recognized. H₂S protects against the hypoxia/reoxygenation (H/R)-induced injury and apoptosis of cardiomyocytes, and ischemic post-conditioning (PC) plays an important role in cardioprotection from H/R injury in neonatal cardiomyocytes but not in aging cardiomyocytes. Whether H₂S is involved in the recovery of PC-induced cardioprotection in aging cardiomyocytes is unclear. In the present study, we found that both H/R and PC decreased cystathionine-γ-lyase (CSE) expression and the production rate of H₂S. Supplementation of NaHS protected against H/R-induced apoptosis, the expression of cleaved caspase-3 and cleaved caspase-9, the release of cytochrome c (Cyt c), and mPTP opening. The addition of NaHS also counteracted the reduction of cell viability caused by H/R and increased the phosphorylation of ERK1/2, PI3K, Akt, GSK-3β and mitochondrial membrane potential. Additionally, NaHS increased Bcl-2 expression, promoted PKC-ε translocation to the cell membrane, and activated mitochondrial ATP-sensitive K channels (mitoK_ATP). PC alone did not provide cardioprotection in H/R-treated aging cardiomyocytes, which was significantly restored by the supplementation of NaHS. In conclusion, our results suggest that exogenous H₂S restores PC-induced cardioprotection via the inhibition of mPTP opening by the activation of the ERK1/2-GSK-3β, PI3K-Akt-GSK-3β and PKC-ε-mitoK_ATP pathways in aging cardiomyocytes. These findings provide a novel target for the treatment of aging ischemic cardiomyopathy.

Protective effect of ischemic postconditioning against hepatic ischemic reperfusion injury in rat liver

Purpose

The efficiency of ischemic postconditioning (IPC) was evaluated in a rat model of ischemic liver. Concentration of survivin of liver tissue correlated with the degree of antiapoptosis, so survivin was estimated to evaluate the efficiency of IPC on ischemic reperfusion (IR) injury.

Methods

Twenty-four healthy rats were divided to three groups (SHAM, IR, and IPC). Rats in the SHAM group displayed no change during 3 hours. Rats in the IR group were ischemic within 1 hour of clamping the left hepatic artery and left portal vein. Reperfusion for 2 hours was then done. IPC group, intermittent 2, 3, 5, and 7 minutes of reperfusion followed by 1 hour of warm ischemia. Two-minute reocclusion was done after each reperfusion. Rat sera were analyzed for AST and ALT, and Western blot analysis of rat liver tissue of rats evaluated malondialdehyde (MDA) and survivin.

Results

MDA in the liver tissue of rats in the IR and IPC group were significantly high than in the liver tissue of the SHAM group (P = 0.003 and P = 0.008, respectively). Survivin was higher in the IPC group than in the SHAM and IR groups (P = 0.021 and P = 0.024, respectively).

Conclusion

IPC could not prevent lipid oxidation in liver cell mitochondria, but did aid in the regeneration of ischemic injured liver cells. The results indicate that IPC can suppress the apoptosis of liver cells and reduce reperfusion injury of liver tissue.

Postconditioning in major vascular surgery: prevention of renal failure

Background

Postconditioning is a novel reperfusion technique to reduce ischemia-reperfusion injuries. The aim of the study was to investigate this method in an animal model of lower limb revascularization for purpose of preventing postoperative renal failure.

Methods

Bilateral lower limb ischemia was induced in male Wistar rats for 3 hours by infrarenal aorta clamping under narcosis. Revascularization was allowed by declamping the aorta. Postconditioning (additional 10 sec reocclusion, 10 sec reperfusion in 6 cycles) was induced at the onset of revascularization. Myocyte injury and renal function changes were assessed 4, 24 and 72 hours postoperatively. Hemodynamic monitoring was performed by invasive arterial blood pressure registering and a kidney surface laser Doppler flowmeter.

Results

Muscle viability studies showed no significant improvement with the use of postconditioning in terms of ischemic rhabdomyolysis (4 h: ischemia-reperfusion (IR) group: 42.93 ± 19.20% vs. postconditioned (PostC) group: 43.27 ± 27.13%). At the same time, renal functional laboratory tests and kidney myoglobin immunohistochemistry demonstrated significantly less expressed kidney injury in postconditioned animals (renal failure index: 4 h: IR: 2.37 ± 1.43 mM vs. PostC: 0.92 ± 0.32 mM; 24 h: IR: 1.53 ± 0.45 mM vs. PostC: 0.77 ± 0.34 mM; 72 h: IR: 1.51 ± 0.36 mM vs. PostC: 0.43 ± 0.28 mM), while systemic hemodynamics and kidney microcirculation significantly improved (calculated reperfusion area: IR: 82.31 ± 12.23% vs. PostC: 99.01 ± 2.76%), and arterial blood gas analysis showed a lesser extent systemic acidic load after revascularization (a defined relative base excess parameter: 1^st s: IR: 2.25 ± 1.14 vs. PostC: 1.80 ± 0.66; 2^nd s: IR: 2.14 ± 1.44 vs. PostC: 2.44 ± 1.14, 3^rd s: IR: 3.99 ± 3.09 vs. PostC: 2.07 ± 0.82; 4^th s: IR: 3.28 ± 0.32 vs. PostC: 2.05 ± 0.56).

Conclusions

The results suggest a protective role for postconditioning in major vascular surgeries against renal complications through a possible alternative release of nephrotoxic agents and exerting a positive effect on hemodynamic stability.

Influence of levosimendan postconditioning on apoptosis of rat lung cells in a model of ischemia-reperfusion injury

Objective

To ascertain if levosimendan postconditioning can alleviate lung ischemia–reperfusion injury (LIRI) in rats.

Method

One hundred rats were divided into five groups: Sham (sham), ischemia–reperfusion group (I/R group), ischemic postconditioning (IPO group), levosimendan postconditioning (Levo group) and combination postconditioning group of levosimendan and 5-Hydroxydecanoic acid (Levo+5-HD group). The apoptotic index (AI) of lung tissue cells was determined using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Expression of active cysteine aspartate specific protease-3 ( active caspase-3), Bcl-2 and Bax in lung tissue was determined by immunohistochemical staining. The morphopathology of lung tissue was observed using light and electron microscopy.

Results

AI values and expression of active caspase-3, Bcl-2 and Bax of lung tissue in I/R and Levo+5-HD groups were significantly higher than those in the sham group ( P<0.05). AI values and expression of active caspase-3 and Bax were significantly lower, whereas that of Bcl-2 was higher significantly in the Levo group, compared with I/R and Levo+5-HD groups (P<0.05). Significant differences were not observed in comparisons between I/R and Levo+5-HD groups as well as IPO and Levo groups.

Conclusion

LIRI can be alleviated by levosimendan, which simulates an IPO protective function. A postulated lung-protective mechanism of action could involve opening of mitochondrial adenosine triphosphate-sensitive potassium channels, relieving Ca2+ overload, upregulation of expression of Bcl-2, and downregulation of expression of active caspase-3 and Bax.

Interrupted reperfusion reduces the activation of NADPH oxidase after cerebral I/R injury

Interrupted reperfusion reduces ischemia/reperfusion (I/R) injury. This study was designed to determine whether NADPH oxidase participates in the neural protection against global I/R injury after interrupted reperfusion. Mice were randomly divided into five groups: sham (sham-operated), I/R (20-min global I/R), RR (I/R+interrupted reperfusion), Apo (I/R+apocynin administration), and RR+Apo. Behavioral tests (pole test, beam walking, and Morris water maze) and Nissl staining were undertaken in all five groups; superoxide levels, expression of gp91(phox) and p47(phox), p47(phox) translocation, and Rac1 activation were measured in the sham, I/R, and RR groups. The motor coordination, bradykinesia, and spatial learning and memory, as well as the neuron survival rates, were better in the RR, Apo, and RR+Apo groups than in the I/R group. The NADPH oxidase-dependent superoxide levels, p47(phox) and gp91(phox) expression, p47(phox) translocation, and Rac1 activation were lower in the RR group than in the I/R group. In conclusion, the neural protective effect of interrupted reperfusion is at least partly mediated by decreasing the expression and assembly of NADPH oxidase and the levels of NADPH oxidase-derived superoxide. The most striking reduction Rac1-GTP in the RR group suggests that interrupted reperfusion also acts on the activation of assembled NADPH oxidase by reducing the availability of Rac1-GTP.

Comparison of cardioprotective and anti-inflammatory effects of ischemia pre- and postconditioning in rats with myocardial ischemia-reperfusion injury

OBJECTIVE

To compare cardioprotective and anti-inflammatory effects of ischemia preconditioning (IPC) and ischemia postconditioning (IPOC) in a rat myocardial ischemia-reperfusion injury (IRI) model.

METHODS

Forty Sprague-Dawley rats were randomly divided equally into four groups. In the groups other than the sham group, the left anterior descending coronary artery was ligated for 30 min followed by a 180 min reperfusion in vivo. The control group was subjected to no additional intervention, the IPC group to three cycles of 5 min ischemia separated by 5 min reperfusion before the index ischemia and the IPOC group to three cycles of 10 s ischemia separated by 10 s reperfusion immediately after the end of the index ischemia. Hemodynamic changes during the ischemia and reperfusion were recorded. At 180 min of reperfusion, serum concentrations of troponin I (TnI), tumor necrosis factor α (TNF-α) and high-mobility group box 1 (HMGB-1) were assayed, and the infarction size was assessed by Evans blue and triphenyltetrazolium chloride staining.

RESULTS

Compared to the control group, infarct size and serum concentrations of TnI, TNF-α and HMGB1 at 180 min of reperfusion were significantly reduced in the IPC and IPOC groups. However, infarct size and serum concentrations of TNF-α and HMGB1 at 180 min of reperfusion were significantly increased in the IPOC group compared to the IPC group.

CONCLUSIONS

In the rats with myocardial IRI in vivo, both IPC and IPOC can produce significant cardioprotective and anti-inflammatory effects. However, cardioprotective and anti-inflammatory effects provided by IPOC are weaker than with IPC.

Potential therapeutic benefits of strategies directed to mitochondria

The mitochondrion is the most important organelle in determining continued cell survival and cell death. Mitochondrial dysfunction leads to many human maladies, including cardiovascular diseases, neurodegenerative disease, and cancer. These mitochondria-related pathologies range from early infancy to senescence. The central premise of this review is that if mitochondrial abnormalities contribute to the pathological state, alleviating the mitochondrial dysfunction would contribute to attenuating the severity or progression of the disease. Therefore, this review will examine the role of mitochondria in the etiology and progression of several diseases and explore potential therapeutic benefits of targeting mitochondria in mitigating the disease processes. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate and manipulate mitochondrial function and genomics for therapeutic benefit. These approaches to treat mitochondrial dysfunction rationally could lead to selective protection of cells in different tissues and various disease states. However, most of these approaches are in their infancy.

Postconditioning of the lower limb--protection against the reperfusion syndrome

BACKGROUND

Postconditioning-alternating brief cycles of reperfusion/reocclusion applied at the beginning of revascularization-is a potent therapeutic technique, attenuating ischemia-reperfusion injury. Vascular surgery on the lower limb with ischemia-reperfusion injury may give rise to serious systemic complications [organ dysfunction syndrome (MODS), systemic inflammatory response syndrome (SIRS)], a phenomenon called reperfusion-syndrome.

MATERIAL AND METHODS

We studied the effects of postconditioning on reperfusion-syndrome in a rodent experimental model. Wistar rats underwent 180 min of bilateral lower limb ischemia using an infrarenal crossclamping of the abdominal aorta. Postconditioning consisted of six cycles of 10-s aortic occlusion/10-s declamping at the beginning of reperfusion. Microcirculation of the lower limb was detected with laser Doppler flowmeter. After 4 h of reperfusion, plasma, urine, and histologic samples were collected.

RESULTS

One hundred eighty-minute ischemia resulted in significant hemodynamic changes after reperfusion. Postconditioning affected the character of the microcirculatory flow, the limb circulation stabilized with hyperemia during reperfusion. Postconditioning caused a significant reduction in systemic inflammatory response (TNF-α, oxygen-derived free radicals). The laboratory and histologic samples implied a significant decrease in distant organ (lung and renal) dysfunctions after postconditioning.

CONCLUSION

Postconditioning proves to be capable of conferring protection against different organ injuries caused by longer circulatory occlusions during elective major vascular operations.