Sequential limb ischemia demonstrates remote postconditioning protection of murine skeletal muscle

Remote ischemic conditioning as a cytoprotective strategy in vasculopathies during hyperhomocysteinemia: An emerging research perspective

Higher levels of nonprotein amino acid homocysteine (Hcy), that is, hyperhomocysteinemia (HHcy) (~5% of general population) has been associated with severe vasculopathies in different organs; however, precise molecular mechanism(s) as to how HHcy plays havoc with body's vascular networks are largely unknown. Interventional modalities have not proven beneficial to counter multifactorial HHcy's effects on the vascular system. An ancient Indian form of exercise called 'yoga' causes transient ischemia as a result of various body postures however the cellular mechanisms are not clear. We discuss a novel perspective wherein we argue that application of remote ischemic conditioning (RIC) could, in fact, deliver anticipated results to patients who are suffering from chronic vascular dysfunction due to HHcy. RIC is the mechanistic phenomenon whereby brief episodes of ischemia-reperfusion events are applied to distant tissues/organs; that could potentially offer a powerful tool in mitigating chronic lethal ischemia in target organs during HHcy condition via simultaneous reduction of inflammation, oxidative and endoplasmic reticulum stress, extracellular matrix remodeling, fibrosis, and angiogenesis. We opine that during ischemic conditioning our organs cross talk by releasing cellular messengers in the form of exosomes containing messenger RNAs, circular RNAs, anti-pyroptotic factors, protective cytokines like musclin, transcription factors, small molecules, anti-inflammatory, antiapoptotic factors, antioxidants, and vasoactive gases. All these could help mobilize the bone marrow-derived stem cells (having tissue healing properties) to target organs. In that context, we argue that RIC could certainly play a savior's role in an unfortunate ischemic or adverse event in people who have higher levels of the circulating Hcy in their systems.

Limb Remote Ischemic Conditioning: Mechanisms, Anesthetics, and the Potential for Expanding Therapeutic Options

Novel and innovative approaches are essential in developing new treatments and improving clinical outcomes in patients with ischemic stroke. Remote ischemic conditioning (RIC) is a series of mechanical interruptions in blood flow of a distal organ, following end organ reperfusion, shown to significantly reduce infarct size through inhibition of oxidation and inflammation. Ischemia/reperfusion (I/R) is what ultimately leads to the irreversible brain damage and clinical picture seen in stroke patients. There have been several reports and reviews about the potential of RIC in acute ischemic stroke; however, the focus here is a comprehensive look at the differences in the three types of RIC (remote pre-, per-, and postconditioning). There are some limited uses of preconditioning in acute ischemic stroke due to the unpredictability of the ischemic event; however, it does provide the identification of biomarkers for clinical studies. Remote limb per- and postconditioning offer a more promising treatment during patient care as they can be harnessed during or after the initial ischemic insult. Though further research is needed, it is imperative to discuss the importance of preclinical data in understanding the methods and mechanisms involved in RIC. This understanding will facilitate translation to a clinically feasible paradigm for use in the hospital setting.

Postischemic conditioning does not reduce muscle injury after tourniquet-induced ischemia-reperfusion injury in rats

BACKGROUND

The widespread application of tourniquets has reduced battlefield mortality related to extremity exsanguinations. Tourniquet-induced ischemia-reperfusion injury (I/R) can contribute to muscle loss. Postischemic conditioning (PostC) confers protection against I/R in cardiac muscle and skeletal muscle flaps. The objective of this study was to determine the effect of PostC on extremity muscle viability in an established rat hindlimb tourniquet model.

METHODS

Rats were randomly assigned to PostC-1, PostC-2, or no conditioning ischemic groups (n = 10 per group). Postischemic conditioning, performed immediately after tourniquet release, consisted of four 15-second cycles (PostC-1) or eight 15-second cycles (PostC-2) of alternating occlusion and perfusion of hindlimbs. Twenty-four hours later, muscles were excised. The primary end points were muscle edema and viability; secondary end points were histologic and markers of oxidative stress.

RESULTS

Ischemia-reperfusion injury decreased viability in all tourniquet limbs, but viability was not improved in either PostC group. Likewise, I/R resulted in substantial muscle edema that was not reduced by PostC. The predominant histologic feature was necrosis, but no significant differences were found among groups. Markers of oxidative stress were increased similarly among groups after I/R, although myeloperoxidase activity was significantly increased only in the no conditioning ischemic group. A protective effect from PostC was not observed in our model suggesting that PostC was not effective in reducing I/R skeletal muscle injury or any benefits of PostC were not sustained for 24 hours when tissues were assessed.

CONCLUSION

These negative findings are pertinent as the military investigates different strategies to extend the safe time for tourniquet application.

Measurement of free radicals using electron paramagnetic resonance spectroscopy during open aorto-iliac arterial reconstruction

BACKGROUND

Aortic cross-clamping during abdominal aortic aneurysm (AAA) open repair leads to development of ischemia-reperfusion injury. Electron paramagnetic resonance spectroscopy (EPR) spin-trapping is a valuable method of direct measurement of free radicals. The objective of the study was to evaluate the results of EPR as a direct method of free radical measurement and degree of inflammatory response in open operative treatment of patients with AAA and aorto-iliac occlusive disease (AIOD).

MATERIAL/METHODS

The study was performed on a group of 32 patients with AAA and 25 patients with AIOD scheduled for open repair. Peripheral venous blood for EPR spectroscopy and for SOD, GPx, ox-LDL, Il-6, TNF-alfa, CRP, and HO-1 were harvested. Selected parameters were established accordingly to specified EPR and immunohistochemical methods and analyzed between groups by Mann-Whitney U test and Wilcoxon matched-pairs signed-ranks test with Bonferroni correction.

RESULTS

Free radicals level was correlated with the time of the aortic cross-clamping after the reperfusion of he first and second leg in AAA (r=0.7; r=0.47). ox-LDL in AAA decreased 5 min after reperfusion of the first leg (32.99 U/L, range: 14.09-77.12) and 5 min after reperfusion of the second leg (26.75 U/L, range: 11.56-82.12) and 24 h after the operation (25.85 U/L, range: 14.29-49.70). HO-1 concentration increased to above the level before intervention 24 h after surgery. The activities of GPx and SOD decreased 5 min after the first-leg reperfusion in AAA. Twenty-four hours after surgery, inflammatory markers increased in AAA to CRP was 14.76 ml/l (0.23-38.55), IL-6 was 141.22 pg/ml (84.3-591.03), TNF-alfa was 6.82 pg/ml (1.76-80.01) and AIOD: CRP was 18.44 mg/l (2.56-33.14), IL-6: 184.1 pg/ml (128.46-448.03), TNF-alfa was 7.74 pg/ml (1.74-74.74).

CONCLUSIONS

EPR spin-trapping demonstrates temporarily elevated level of free radicals in early phase of reperfusion, leading to decrease antioxidants in AAA. Elevated free radical levels decreased 24 h after surgery due to various endogenous antioxidants and therapies.

The science and clinical translation of remote postconditioning

The treatment of reperfusion injury requires measures beyond timely reperfusion. Conventional postconditioning (PostC) of ischemic tissues offers a strategy to reduce reperfusion injury, but its adoption is challenged by requiring access and imposing additional ischemia to the ischemic organ. Generating protective signals by PostC in a tissue remote from the target organ such as the limb, i.e. remote PostC (rPostC), may present an alternative approach to exerting endogenous tissue protection. Because rPostC is only recently reported, the fundamental biology of rPostC is not well understood, and studies to date are largely observational. rPostC has been observed to reduce ischemia-reperfusion injury experimentally in heart, kidney, brain and skeletal muscle in multiple species, including rat, rabbit and pig. Both necrosis and apoptosis are reduced. As in remote ischemic preconditioning, rPostC requires a transfer or communication of protective factors or signals through humoral and/or neural pathways. Triggers of target organ protection include G-protein-coupled receptor ligands, metabolites of ischemia, or small thermolabile molecules. Some evidence suggests that reperfusion injury salvage kinases may be involved in rPostC, in agreement with both preconditioning and conventional PostC. Clinical studies investigating improvements in clinical outcomes or biomarkers with rPostC are encouraging.

nNOS and p-ERK involvement in the neuroprotection exerted by remote postconditioning in rats subjected to transient middle cerebral artery occlusion

It has recently been hypothesized that a sub-lethal ischemic insult induced in one organ is able to protect from a harmful ischemia occurring in a different organ. The objective of this study is to identify new putative mechanisms of neuroprotection elicited by remote ischemic femoral postconditioning. A 50% reduction in the infarct volume was observed when 100min of middle cerebral artery occlusion was followed, 10min later, by the remote postconditioning stimulus represented by 20min of femoral artery occlusion. The use of in vivo silencing strategy allowed to demonstrate that NO production through nNOS mediates part of the neuroprotection. Indeed, whereas CNS nNOS expression was up-regulated by remote postconditioning, the pharmacological inhibition of nNOS or its silencing-mediated knocking-down partially prevented this neuroprotective effect. This nNOS overexpression seemed to be p-ERK dependent. In fact, p-ERK expression increased in brain cortex after remote postconditioning, and its pharmacological inhibition prevented both nNOS overexpression and remote postconditioning-mediated neuroprotection. Interestingly, neuroprotection induced by remote postconditioning was partially prevented when ganglion transmission was pharmacologically interrupted by hexamethonium, thus showing that neural factors are involved in this phenomenon. Collectively, the present study demonstrates that p-ERK and nNOS take part to the complex cascade of events triggered by ischemic remote postconditioning.

Remote ischemic conditioning: from bench to bedside

Remote ischemic conditioning (RIC) is a therapeutic strategy for protecting organs or tissue against the detrimental effects of acute ischemia-reperfusion injury (IRI). It describes an endogenous phenomenon in which the application of one or more brief cycles of non-lethal ischemia and reperfusion to an organ or tissue protects a remote organ or tissue from a sustained episode of lethal IRI. Although RIC protection was first demonstrated to protect the heart against acute myocardial infarction, its beneficial effects are also seen in other organs (lung, liver, kidney, intestine, brain) and tissues (skeletal muscle) subjected to acute IRI. The recent discovery that RIC can be induced non-invasively by simply inflating and deflating a standard blood pressure cuff placed on the upper arm or leg, has facilitated its translation into the clinical setting, where it has been reported to be beneficial in a variety of cardiac scenarios. In this review article we provide an overview of RIC, the potential underlying mechanisms, and its potential as a novel therapeutic strategy for protecting the heart and other organs from acute IRI.

Effect of postconditioning on mitochondrial dysfunction in experimental aortic cross-clamping

Background

Cross-clamping of the aorta during abdominal aortic aneurysm surgery induces muscle ischaemia with resultant morbidity. This study tested whether ischaemic postconditioning would decrease mitochondrial dysfunction in skeletal muscle by reducing oxidative stress.

Methods

Three groups (9 rats each) underwent surgery, including a control group without ischaemia and an ischaemia–reperfusion group that had 3 h ischaemia induced by aortic clamping and collateral vessel ligation, followed by 2 h of reperfusion. The third group had ischaemia for 3 h then underwent postconditioning comprising three short intervals of ischaemia–reperfusion at the onset of reperfusion. Activity of complexes I, II, III and IV of the mitochondrial respiratory chain was monitored in gastrocnemius muscle, along with oxidative stress measured by dihydroethidium (DHE) staining and antioxidant defence determined by measurement of glutathione levels.

Results

Ischaemia–reperfusion alone caused a significant reduction in maximal oxidative capacity (−31·8 per cent; P = 0·002), activity of complexes II, III and IV (−34·5 per cent; P = 0·007) and complex IV activity (−30·6 per cent; P = 0·039). It also increased reactive oxygen species (DHE staining increased to 223·1 per cent of control value; P = 0·027) and reduced antioxidant defence (glutathione level − 28·6 per cent; P = 0·039). Postconditioning counteracted these deleterious effects by increasing mitochondrial complex I, II, III and IV activities, restoring muscle DHE staining and preserving glutathione content.

Conclusion

Ischaemic postconditioning protects skeletal muscle mitochondria against ischaemia–reperfusion injury by reducing oxidative stress and preserving antioxidant defence in an experimental model. Mitochondrial protection to reduce reperfusion injury in clinical vascular surgery may be warranted.