Regional ischemic 'preconditioning' protects remote virgin myocardium from subsequent sustained coronary occlusion

Protective effect of remote ischemic pre-conditioning on patients undergoing cardiac bypass valve replacement surgery: A randomized controlled trial

Remote ischemic pre-conditioning (RIPC) may have a protective effect on myocardial injury associated with cardiac bypass surgery (CPB). The objective of the present study was to investigate the effect of RIPC on ischemia/reperfusion (I/R) injury and to assess the underlying mechanisms. A total of 241 patients who underwent valve replacement were randomly assigned to receive either RIPC (n=121) or control group (n=120). The primary endpoint was peri-operative myocardial injury (PMI), which was determined by serum Highly sensitive cardiac troponin T (hsTnT). The secondary endpoint was the blood gas indexes, acute lung injury and length of intensive care unit stay, length of hospital stay and major adverse cardiovascular events. The results indicated that in comparison with control group, RIPC treatment reduced the levels of hsTnT at 6 and 24 h post-CPB (P<0.001), as well as the alveolar-arterial oxygen pressure difference and respiratory index after CPB. Furthermore, RIPC reduced the incidence of acute lung injury by 15.3% (54.1% in the control group vs. 41.3% in the RIPC group, P=0.053). It was indicated that RIPC provided myocardial and pulmonary protection during CPB. In addition, the length of the intensive care unit and hospital stay was reduced by RIPC. Mechanistic investigation revealed a reduced content of soluble intercellular adhesion molecule-1, endothelin-1 and malondialdehyde, as well as elevated levels of nitric oxide in the RIPC group compared with those in the control group. This indicated that RIPC protected against I/R injury associated with CPB through reducing the inflammatory response and oxidative damage, as well as improving pulmonary vascular tension. In conclusion, RIPC reduced myocardial and pulmonary injury associated with CPB. This protective effect may be associated with the inhibition of the inflammatory response and oxidative injury. The present study proved the efficiency of this approach in reducing ischemia/reperfusion injury associated with cardiac surgery. Clinical trial registry no. ChiCTR1800015393.

The Role of O-GlcNAcylation for Protection against Ischemia-Reperfusion Injury

Ischemia reperfusion injury (IR injury) associated with ischemic heart disease contributes significantly to morbidity and mortality. O-linked β-N-acetylglucosamine (O-GlcNAc) is a dynamic posttranslational modification that plays an important role in numerous biological processes, both in normal cell functions and disease. O-GlcNAc increases in response to stress. This increase mediates stress tolerance and cell survival, and is protective. Increasing O-GlcNAc is protective against IR injury. Experimental cellular and animal models, and also human studies, have demonstrated that protection against IR injury by ischemic preconditioning, and the more clinically applicable remote ischemic preconditioning, is associated with increases in O-GlcNAc levels. In this review we discuss how the principal mechanisms underlying tissue protection against IR injury and the associated immediate elevation of O-GlcNAc may involve attenuation of calcium overload, attenuation of mitochondrial permeability transition pore opening, reduction of endoplasmic reticulum stress, modification of inflammatory and heat shock responses, and interference with established cardioprotective pathways. O-GlcNAcylation seems to be an inherent adaptive cytoprotective response to IR injury that is activated by mechanical conditioning strategies.

Sevoflurane, Propofol and Carvedilol Block Myocardial Protection by Limb Remote Ischemic Preconditioning

The effects of remote ischemic preconditioning (RIPC) in cardiac surgery have been inconsistent. We investigated whether anesthesia or beta-blockers interfere with RIPC cardioprotection. Fifty patients undergoing cardiac surgery were randomized to receive limb RIPC (four cycles of 5-min of upper arm cuff inflation/deflation) in the awake state (no-anesthesia; n = 17), or under sevoflurane (n = 17) or propofol (n = 16) anesthesia. In a separate crossover study, 11 healthy volunteers received either carvedilol or no medication prior to RIPC. Plasma dialysates were obtained and perfused through an isolated male Sprague⁻Dawley rat heart subjected to 30-min ischemia/60-min reperfusion, following which myocardial infarct (MI) size was determined. In the cardiac surgery study, pre-RIPC MI sizes were similar among the groups (39.7 ± 4.5% no-anesthesia, 38.9 ± 5.3% sevoflurane, and 38.6 ± 3.6% propofol). However, post-RIPC MI size was reduced in the no-anesthesia group (27.5 ± 8.0%; p < 0.001), but not in the anesthesia groups (35.7 ± 6.9% sevoflurane and 35.8 ± 5.8% propofol). In the healthy volunteer study, there was a reduction in MI size with RIPC in the no-carvedilol group (41.7 ± 4.3% to 30.6 ± 8.5%; p < 0.0001), but not in the carvedilol group (41.0 ± 4.0% to 39.6 ± 5.6%; p = 0.452). We found that the cardioprotective effects of limb RIPC were abolished under propofol or sevoflurane anesthesia and in the presence of carvedilol therapy.

Circulating mediators of remote ischemic preconditioning: search for the missing link between non-lethal ischemia and cardioprotection

Acute myocardial infarction (AMI) is one of the leading causes of mortality and morbidity worldwide. There has been an extensive search for cardioprotective therapies to reduce myocardial ischemia-reperfusion (I/R) injury. Remote ischemic preconditioning (RIPC) is a phenomenon that relies on the body's endogenous protective modalities against I/R injury. In RIPC, non-lethal brief I/R of one organ or tissue confers protection against subsequent lethal I/R injury in an organ remote to the briefly ischemic organ or tissue. Initially it was believed to be limited to direct myocardial protection, however it soon became apparent that RIPC applied to other organs such as kidney, liver, intestine, skeletal muscle can reduce myocardial infarct size. Intriguing discoveries have been made in extending the concept of RIPC to other organs than the heart. Over the years, the underlying mechanisms of RIPC have been widely sought and discussed. The involvement of blood-borne factors as mediators of RIPC has been suggested by a number of research groups. The main purpose of this review article is to summarize the possible circulating mediators of RIPC, and recent studies to establish the clinical efficacy of these mediators in cardioprotection from lethal I/R injury.

Effects of remote ischemic preconditioning on astrocyte proliferation and glial scars after cerebral infarction

The aim of this study was to investigate whether remote ischemic preconditioning (RIPC) can promote neurological function recovery after middle cerebral artery occlusion (MCAO) in rats and its possible mechanism. A total of 32 Sprague Dawley (SD) rats were randomly divided into RIPC group (n = 16) and MCAO group (n = 16). In the RIPC group, 1 h before induction of MCAO, the rats received bilateral femoral artery ischemic preconditioning (10 min/time), followed by 10 min of relaxation, and a total of three cycles were carried out. Then, the MCAO-2h model was established. In the MCAO group, the MCAO-2h model was established at 1 h after the separation of bilateral femoral arteries. The modified neurological severity score (mNSS) was assessed. At postmodeling day 7, triphenyltetrazolium chloride (TTC) staining and immunohistochemistry were conducted, and neurological function recovery, infarct size, and the expression levels of glial fibrillary acidic protein (GFAP), synaptophysin (SYN), and neurite outgrowth inhibitor A (Nogo-A) were observed. At postmodeling day 7, the difference in mNSS was statistically significant ( P < 0.05). Infarct size was significantly smaller in the RIPC group than in the MCAO group ( P < 0.05). The number of GFAP+ cells was significantly lesser in the RIPC group than in the MCAO group ( P < 0.05). The difference in thickness of the glial scar was not statistically significant ( P = 0.091). At postmodeling day 7, the expression level of SYN integrated optical density (IOD) was significantly higher in the RIPC group than in the MCAO group ( P < 0.05). The number of Nogo-A+ cells was significantly lesser in the RIPC group than in the MCAO group ( P < 0.05). At day 7 after MCAO, RIPC can promote neurological function recovery in rats and reduce infarct size. The mechanism may be that after 7 days, RIPC reduces GFAP expression, inhibits the trend of glial scar formation and Nogo-A expression, and increases SYN expression.

Cortisol Response in Children After Second Cardiopulmonary Bypass

A surge in cortisol levels is seen after surgery with cardiopulmonary bypass (CPB). Based on evidence of attenuation of the cortisol response to repeated stress in other settings, we hypothesized that the magnitude of cortisol increase in children after a second exposure to CPB would be reduced. Serial cortisol levels were measured at three time points after each CPB: immediately (day 0), on the first morning (day 1), and second morning (day 2). Forty-six children underwent two surgeries with CPB during the study period. The mean age (standard deviation) at first and second surgery was 3.5 (6.3) months and 10.4 (9.9) months, respectively. Cortisol levels at the first surgery were 109 (105) µg/dl, 29 (62) µg/dl, and 17 (12) µg/dl on day 0, 1, and 2, respectively; similarly at second surgery, it was 61 (57) µg/dl on day 0 to 20 (16) µg/dl and 11 (10) µg/dl on day 1 and 2, respectively. After log-transformation and adjusting for time interval between surgeries, cortisol levels at the second surgery were lower by 42% on day 0 (p = 0.02), and 46% lower on day 2 (p = 0.02). A second exposure to CPB in children with congenital heart disease is associated with an attenuated cortisol release.

Exercise and Cardioprotection: A Natural Defense Against Lethal Myocardial Ischemia-Reperfusion Injury and Potential Guide to Cardiovascular Prophylaxis

Similar to ischemic preconditioning, high-intensity exercise has been shown to decrease infarct size following myocardial infarction. In this article, we review the literature on beneficial effects of exercise, exercise requirements for cardioprotection, common methods utilized in laboratories to study this phenomenon, and discuss possible mechanisms for exercise-mediated cardioprotection.

Molecular Mechanism of Ischaemic Preconditioning of Skeletal Muscle In Vitro

Introduction

Ischaemic preconditioning (IPC) is a phenomenon whereby tissues develop an increased tolerance to ischaemia and subsequent reperfusion if first subjected to sublethal periods of ischaemia. Despite extensive investigation of IPC, the molecular mechanism remains largely unknown. Our aim was to show genetic changes that occur in skeletal muscle cells in response to IPC.

Methods

We established an in vitro model of IPC using a human skeletal muscle cell line. Gene expression of both control and preconditioned cells at various time points was determined. The genes examined were hypoxia-inducible factor-1 alpha (HIF-1 alpha), early growth response 1 (EGR1), JUN, and FOS. HIF-1 alpha is a marker of hypoxia. EGR1, JUN, and FOS are early response genes and may play a role in the protective responses induced by IPC.

Results

HIF-1 alpha was upregulated following one and two hours of simulated ischaemia (p = 0.076 and 0.841, respectively) verifying that hypoxic conditions were met using our model. Expression of EGR1 and FOS was upregulated and peaked after one hour of hypoxia (p = 0.001 and <0.00, respectively). cFOS was upregulated at two and three hours of hypoxia. IPC prior to simulated hypoxia resulted in a greater level of upregulation of EGR1, JUN and FOS genes (p = <0.00, 0.047, and <0.00 respectively).

Conclusion

This study has supported the use of our hypoxic model for studying IPC in vitro. IPC results in a greater upregulation of protective genes in skeletal muscle cells exposed to hypoxia than in control cells. We have demonstrated hitherto unknown molecular mechanisms of IPC in cell culture.

Cardioprotection via the skin: nociceptor-induced conditioning against cardiac MI in the NIC of time

Timely reperfusion is still the most effective approach to limit infarct size in humans. Yet, despite advances in care and reduction in door-to-balloon times, nearly 25% of patients develop heart failure postmyocardial infarction, with its attendant morbidity and mortality. We previously showed that cardioprotection results from a skin incision through the umbilicus in a murine model of myocardial infarction. In the present study, we show that an electrical stimulus or topical capsaicin applied to the skin in the same region induces significantly reduced infarct size in a murine model. We define this class of phenomena as nociceptor-induced conditioning (NIC) based on the peripheral nerve mechanism of initiation. We show that NIC is effective both as a preconditioning and postconditioning remote stimulus, reducing infarct size by 86% and 80%, respectively. NIC is induced via activation of skin C-fiber nerves. Interestingly, the skin region that activates NIC is limited to the anterior of the T9-T10 vertebral region of the abdomen. Cardioprotection after NIC requires the integrity of the spinal cord from the region of stimulation to the thoracic vertebral region of the origin of the cardiac nerves but does not require that the cord be intact in the cervical region. Thus, we show that NIC is a reflex and not a central nervous system-mediated effect. The mechanism involves bradykinin 2 receptor activity and activation of PKC, specifically, PKC-α. The similarity of the neuroanatomy and conservation of the effectors of cardioprotection supports that NIC may be translatable to humans as a nontraumatic and practical adjunct therapy against ischemic disease. NEW & NOTEWORTHY This study shows that an electrical stimulus to skin sensory nerves elicits a very powerful cardioprotection against myocardial infarction. This stimulus works by a neurogenic mechanism similar to that previously elucidated for remote cardioprotection of trauma. Nociceptor-induced conditioning is equally potent when applied before ischemia or at reperfusion and has great potential clinically.

Seven consecutive days of remote ischaemic preconditioning improves cutaneous vasodilatory capacity in young adults

KEY POINTS

Remote ischaemic preconditioning (RIPC), induced by brief bouts of ischaemia followed by reperfusion, confers vascular adaptations that protect against subsequent bouts of ischaemia; however, the effect of RIPC repeated over several days on the human microcirculation is unknown. Using skin as a model, microvascular function was assessed at a control and a NO-inhibited area of skin before 1 day after and 1 week after administering seven consecutive days of repeated RIPC on the contralateral arm. Maximal vasodilatation was increased by ∼20-50% following 7 days of repeated RIPC, and this response remained elevated 1 week after stopping RIPC; however, NO-mediated vasodilatation was not affected by the RIPC stimulus. These data indicate that repeated RIPC augments maximal vasodilatation, but the underlying mechanism for this improvement is largely independent of NO. This finding suggests a role for other endothelium-derived mediators and/or for endothelium-independent adaptations with repeated RIPC.

ABSTRACT

Remote ischaemic preconditioning (RIPC), induced by intermittent periods of ischaemia followed by reperfusion, confers cardiovascular protection from subsequent ischaemic bouts. RIPC increases conduit and resistance vessel function; however, the effect of RIPC on the microvasculature remains unclear. Using human skin as a microvascular model, we hypothesized that cutaneous vasodilatory (VD) function elicited by localized heating would be increased following repeated RIPC. Ten participants (23 ± 1 years, 6 males, 4 females) performed RIPC for seven consecutive days. Each daily RIPC session consisted of 4 repetitions of 5 min of arm blood flow occlusion interspersed by 5 min reperfusion. Before, 1 day after and 1 week after the 7 days of RIPC, two microdialysis fibres were placed in ventral forearm skin for continuous infusion of Ringer solution or 20 mM l-NAME. Red blood cell flux was measured by laser Doppler flowmetry at each fibre site during local heating (T_loc  = 39°C) and during maximal VD elicited by heating (T_loc  = 43°C) and 28 mM sodium nitroprusside infusion. Data were normalized to cutaneous vascular conductance (flux/mmHg). Seven days of RIPC did not alter the nitric oxide (NO) contribution to the VD response to local heating (P > 0.05). However, the maximal VD was augmented (Pre: 2.5 ± 0.2, Post: 3.8 ± 0.5 flux/mmHg; P < 0.05) and remained elevated 1 week post RIPC (3.3 ± 0.4 flux/mmHg; P < 0.05). Repeated RIPC improves maximal VD but does not affect NO-mediated VD in the cutaneous microvasculature. This finding suggests that other factors may explain the vasodilatory adaptations that occur following repeated RIPC.

Beneficial effects of remote organ ischemic preconditioning on micro-rheological parameters during liver ischemia-reperfusion in the rat

BACKGROUND

Remote ischemic preconditioning (RIPC) can be protective against the damage. However, there is no consensus on the optimal amount of tissue, the number and duration of the ischemic cycles, and the timing of the preconditioning. The hemorheological background of the process is also unknown.

OBJECTIVE

To investigate the effects of remote organ ischemic preconditioning on micro-rheological parameters during liver ischemia-reperfusion in rats.

METHODS

In anesthetized rats 60-minute partial liver ischemia was induced with 120-minute reperfusion (Control, n = 7). In the preconditioned groups a tourniquet was applied on the left thigh for 3×10 minutes 1 hour (RIPC-1, n = 7) or 24 hours (RIPC-24, n = 7) prior to the liver ischemia. Blood samples were taken before the operation and during the reperfusion. Acid-base, hematological parameters, erythrocyte aggregation and deformability were tested.

RESULTS

Lactate concentration significantly increased by the end of the reperfusion. Erythrocyte deformability was improved in the RIPC-1 group, erythrocyte aggregation increased during the reperfusion, particularly in the RIPC-24 group.

CONCLUSIONS

RIPC alleviated several hemorheological changes caused by the liver I/R. However, the optimal timing of the RIPC cannot be defined based on these results.

Targeting HIF-1α to Prevent Renal Ischemia-Reperfusion Injury: Does It Work?

Partial nephrectomy (open or minimally invasive) usually requires temporary renal arterial occlusion to limit intraoperative bleeding and improve access to intrarenal structures. This is a time-critical step due to the critical ischemia period of renal tissue. Prolonged renal ischemia may lead to irreversible nephron damage in the remaining tissue and, ultimately, chronic kidney disease. This is potentiated by the incompletely understood ischemia-reperfusion injury (IRI). A key mechanism in IRI prevention appears to be the upregulation of an intracellular transcription protein, Hypoxia-Inducible Factor (HIF). HIF mediates metabolic adaptation, angiogenesis, erythropoiesis, cell growth, survival, and apoptosis. Upregulating HIF-1α via ischemic preconditioning (IPC) or drugs that simulate hypoxia (hypoxia-mimetics) has been investigated as a method to reduce IRI. While many promising chemical agents have been trialed for the prevention of IRI in small animal studies, all have failed in human trials. The aim of this review is to highlight the techniques and drugs that target HIF-1α and ameliorate IRI associated with renal ischemia. Developing a technique or drug that could reduce the risk of acute kidney injury associated with renal IRI would have an immediate worldwide impact on multisystem surgeries that would otherwise risk ischemic tissue injury.

Remote ischemic conditioning for stroke: clinical data, challenges, and future directions

Despite great improvement during the past several decades, the management of stroke is still far from satisfactory, which warrants alternative or adjunctive strategies. Remote ischemic conditioning (RIC), an easy‐to‐use and noninvasive therapy, can be performed in various clinical scenarios (e.g., prehospital transportation, intrahospital, and at home), and it has been widely investigated for stroke management. RIC has been demonstrated to be well tolerated in patients with acute ischemic stroke and aneurysm subarachnoid hemorrhage, and it may benefit these patients by improving clinical outcomes; in patients with intracranial atherosclerosis, long‐term repeated RIC could be safely performed and benefit patients by reducing recurrent ischemic stroke and transient ischemic attack, as well as improving cerebral perfusion status; long‐term repeated RIC may also benefit patients with cerebral small vessel disease by slowing cognitive decline and reducing volume of white matter hyperintensities on brain MRI; in patients with severe carotid atherosclerotic stenosis undergoing stenting, preprocedural RIC could reduce the odds of new brain lesions on postprocedural MRI. Previous clinical studies suggest broad future prospects of RIC in the field of cerebrovascular diseases. However, the optimal RIC protocol and the mechanisms that RIC protects the brain is not fully clear, and there is lack of sensitive and specific biomarkers of RIC, all these dilemmas prevent RIC from entering clinical practice. This review focuses on recent advances in clinical studies of RIC in stroke management, its challenges, and the potential directions of future studies.

Effects of Ischemic Preconditioning on Abdominal Aortic Aneurysm Repair: A Systematic Review and Meta-analysis

BACKGROUND

Ischemic preconditioning is an innate mechanism of cytoprotection against ischemia, with potential for end-organ protection. The primary goal of this study was to systematically review the literature to determine the effect of ischemic preconditioning on outcomes after open and endovascular abdominal aortic aneurysm (AAA) repair.

METHODS

The methodology followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. We included randomized clinical trials that evaluated the effect of remote ischemic preconditioning (RIPC) in reducing morbidity and mortality in patients undergoing open or endovascular AAA repair surgery. The primary outcomes were death, myocardial infarction, and renal impairment. Outcomes were addressed separately for open AAA repair and endovascular AAA repair (EVAR). Data were collected on patient characteristics, methodology, and preconditioning protocol for each trial.

RESULTS

Nine trials of ischemic preconditioning in aortic aneurysm surgery were included with a total of 599 patients; 336 patients were included in the open AAA repair meta-analysis, and 263 patients were included in the EVAR meta-analysis. For both open and endovascular repairs, ischemic preconditioning did not have a significant effect on death, myocardial infarction, or renal impairment requiring dialysis.

CONCLUSIONS

The randomized clinical trials investigating the effect of ischemic preconditioning on outcomes after open and endovascular AAA repair that have been completed to date have not been adequately powered to evaluate improvements in patient-important outcomes. The evidence is insufficient to support the use of ischemic preconditioning for AAA repair in clinical practice. The variability in treatment effect across studies may be explained by clinical and methodological heterogeneity.

Short-Term Glucocorticoid Treatment Normalizes the Microcirculatory Response to Remote Ischemic Conditioning in Early Complex Regional Pain Syndrome

BACKGROUND

The early phase of complex regional pain syndrome (CRPS) is characterized by an inflammatory state and therefore often treated with anti-inflammatory acting glucocorticoids. Recently, we demonstrated that remote ischemic conditioning (RIC), a cyclic application of nondamaging ischemia on a remote extremity, reduces blood flow and increases oxygen extraction in the CRPS-affected extremity.

AIM

The aim of the presented study was to analyze the effect of short-term pain treatment including glucocorticoid pulse treatment on the RIC-induced perfusion parameters.

METHOD

Independently from the study, pain treatment was started with an oral glucocorticoid pulse (180 to 360 mg prednisolone) in 12 patients with CRPS (disease duration < 1 year). RIC was conducted before and after pulse treatment. Three cycles of 5 minutes ischemia and 10 minutes reperfusion were applied to the contralateral limb. Blood flow, tissue oxygenation, and oxygen extraction fraction were assessed ipsilateral before and during RIC. Current pain was assessed on the numeric rating scale (0 to 10), and finger-palm distance was measured.

RESULTS

Pain level (5.8 ± 1.5 vs. 3.1 ± 1.1) and finger-palm distance (5 ± 1.9 cm vs. 3.7 ± 1.9 cm) were decreased significantly by the treatment. RIC decreased blood flow by 32.8% ± 42.8% (P < 0.05) and increased oxygen extraction fraction by 8.5% ± 10.3% (P < 0.05) solely before the treatment. After treatment, all parameters remained unchanged after RIC (P < 0.05 vs. before), comparable to healthy subjects.

CONCLUSION

Confirming previous results, RIC presumably unmasks luxury perfusion in untreated CRPS patients. In accordance with the clinical improvement, the short-term pain treatment with glucocorticoids as major component normalizes impaired perfusion. These results might underline the rationale for anti-inflammatory treatment in early-phase CRPS.

Data on the effects of remote ischemic preconditioning in the lungs after one-lung ventilation

This article contains data on experimental endpoints of a randomized controlled animal trial. Fourteen healthy piglets underwent mechanical ventilation including injurious one-lung ventilation (OLV), seven of them experienced four cycles of remote ischemic preconditioning (RIP) on one hind limb immediately before OLV, seven of them did not receive RIP and served as controls, in a randomized manner. The two major endpoints were (1) pulmonary damage assessed with the diffuse alveolar damage (DAD) score and (2) the inflammatory response assessed by cytokine concentrations in serum and in bronchoalveolar lavage fluids (BAL). The cytokine levels in the homogenized lung tissue samples are presented in the original article. Further interpretation and discussion of these data can be found in Bergmann et al. (in press).

Remote Ischemic Pre-conditioning in the Management of Intermittent Claudication: A Pilot Randomized Controlled Trial

BACKGROUND

Animal data suggest that remote ischemic conditioning (RIC) can improve blood flow in ischemic limbs and, consequently, may benefit claudication patients. Supervised exercise is the preferred first-line intervention for patients with intermittent claudication (IC) but is constrained by limited availability and logistical issues, particularly in rural settings. The aim of this study is to evaluate remote ischemic pre-conditioning in the management of intermittent claudication patients.

METHODS

We undertook a randomized clinical trial to evaluate RIC's effect in claudication patients. Stable IC patients were randomly allocated to receive RIC alone, structured exercise (SE) alone, RIC plus SE, or to a control group which received standard advice and risk factor modification. Patients received their intervention over a 28-day period. RIC patients attended an RIC clinic every 3-4 days to undergo 4 cycles of 5-min upper limb ischemia followed by 5-min reperfusion induced with a standard blood pressure cuff.

RESULTS

Forty-five patients were randomized, of whom 40 completed the trial (10 patients per group). The RIC alone, SE alone, and RIC plus SE groups all demonstrated significant improvements in pain-free walking distance and ankle-brachial pressure indices at 30 days. There were no differences in the magnitude of improvements between the groups.

CONCLUSIONS

Compared with standard care RIC is promising as a home-delivered intervention. It appears to be equivalent to SE in the treatment of IC, with no apparent additive benefit to combining the 2 interventions in this small size sample. Large-scale randomized controlled trial is needed for validation.

Acquired Resilience: An Evolved System of Tissue Protection in Mammals

This review brings together observations on the stress-induced regulation of resilience mechanisms in body tissues. It is argued that the stresses that induce tissue resilience in mammals arise from everyday sources: sunlight, food, lack of food, hypoxia and physical stresses. At low levels, these stresses induce an organised protective response in probably all tissues; and, at some higher level, cause tissue destruction. This pattern of response to stress is well known to toxicologists, who have termed it hormesis. The phenotypes of resilience are diverse and reports of stress-induced resilience are to be found in journals of neuroscience, sports medicine, cancer, healthy ageing, dementia, parkinsonism, ophthalmology and more. This diversity makes the proposing of a general concept of induced resilience a significant task, which this review attempts. We suggest that a system of stress-induced tissue resilience has evolved to enhance the survival of animals. By analogy with acquired immunity, we term this system 'acquired resilience'. Evidence is reviewed that acquired resilience, like acquired immunity, fades with age. This fading is, we suggest, a major component of ageing. Understanding of acquired resilience may, we argue, open pathways for the maintenance of good health in the later decades of human life.

Remote ischemic conditioning protects against endothelial ischemia-reperfusion injury via a glucagon-like peptide-1 receptor-mediated mechanism in humans

BACKGROUND

Remote ischemic conditioning (RIC), i.e. short cycles of ischemia and reperfusion in remote tissue, is a novel approach to protect against myocardial ischemia-reperfusion injury in ST-elevation myocardial infarction. The nature of the factors transmitting the protective effect of RIC remains unknown, and both neuronal and hormonal mechanisms appear to be involved. A recent study indicated involvement of glucagon-like peptide-1 (GLP-1) regulated by the vagal nerve in RIC in rats. In the present study we aimed to investigate whether the protective effect of RIC is mediated by a GLP-1 receptor-dependent mechanism in humans.

METHODS

Endothelial function was determined from flow-mediated dilatation (FMD) of the brachial artery before and after 20 min of forearm ischemia and 20 min of reperfusion in twelve healthy subjects on three occasions: (A) ischemia-reperfusion without intervention, (B) ischemia-reperfusion + RIC and (C) iv administration of the GLP-1 receptor antagonist exendin(9-39) + ischemia-reperfusion + RIC.

RESULTS

Ischemia-reperfusion reduced FMD from 4.7 ± 0.8% at baseline to 1.5 ± 0.4% (p < 0.01). RIC protected from the impairment in FMD induced by ischemia-reperfusion (4.6 ± 1.1% at baseline vs. 5.0 ± 1.1% following ischemia-reperfusion). Exendin(9-39) abolished the protection induced by RIC (FMD 4.9 ± 0.9% at baseline vs. 1.4 ± 1.3% following ischemia-reperfusion; p < 0.01) but did not affect basal FMD. Plasma GLP-1 levels did not change significantly between examinations.

CONCLUSION

The present study is the first to suggest that RIC protects against endothelial ischemia-reperfusion injury via a GLP-1 receptor-mediated mechanism in humans.

Remote ischaemic conditioning for prevention of acute kidney injury after valvular heart surgery: a randomised controlled trial

BACKGROUND

Repeated remote ischaemic conditioning (RIC) during weaning from cardiopulmonary bypass and in the early postoperative period may confer protection against acute kidney injury (AKI). We evaluated the effect of repeated RIC on the incidence of AKI in patients undergoing valvular heart surgery.

METHODS

Patients were randomised into either the RIC (n=120) or control (n=124) group. A pneumatic tourniquet was placed on each patient's thigh. Upon removal of the aortic cross-clamp, three cycles of inflation for 5 min at 250 mm Hg (with 5 min intervals) were applied in the RIC group. Additionally, three cycles of RIC were repeated at postoperative 12 and 24 h. AKI was diagnosed based on the Kidney Disease: Improving Global Outcomes guideline. The incidences of renal replacement therapy, permanent stroke, sternal wound infection, newly developed atrial fibrillation, mechanical ventilation >24 h, and reoperation for bleeding during hospitalisation were recorded.

RESULTS

The incidences of AKI were not significantly different between the control (19.4%) and RIC (15.8%) groups (a difference of 3.5 percentage points; 95% confidence interval: -6.8%-13.9%; P=0.470). Perioperative serum creatinine concentrations were similar in the control and RIC groups (P=0.494). Fluid balance, urine output, blood loss, transfusion, and vasopressor/inotropic requirements were not significantly different between the groups (all P>0.05). The occurrences of a composite of morbidity and mortality endpoints were not significantly different between the control (46.0%) and RIC (39.2%) groups (a difference of 6.8 percentage points; 95% confidence interval: -6.4%-20.0%; P=0.283).

CONCLUSIONS

The results of our study do not support repeated RIC to decrease the incidence of AKI after valvular heart surgery.

CLINICAL TRIAL REGISTRATION

NCT02720549.

Preconditioning the uterine unfolded protein response maintains non-apoptotic Caspase 3-dependent quiescence during pregnancy

The prevention of apoptotic caspase 3 activation through biological preconditioning, mediated through the modulation of the unfolded protein response has been demonstrated to ameliorate multiple pathophysiologies. The maintenance of non-apoptotic caspase 3 activity by the unfolded protein response within the pregnant uterus has previously been proven to be critical in inhibiting uterine myocyte contractility during pregnancy. Here we report that the pregnant uterus utilizes an unfolded protein response-preconditioning paradigm to conserve myometrial caspase 3 in a non-apoptotic state in order to effectively inhibit uterine contractility thereby preventing the onset of preterm labor. In the absence of appropriate endogenous preconditioning during pregnancy, uterine caspase 3 is transformed from a non-apoptotic to an apoptotic phenotype. Apoptotic caspase 3 activation results in the precocious triggering of local uterine inflammatory signaling and prostaglandin production, consequently resulting in an increased incidence of preterm birth. These findings represent a paradigm shift in our understanding of how preconditioning promotes the maintenance of uterine non-apoptotic caspase 3 action during pregnancy preventing the onset of premature uterine contraction and therefore defining the timing of the onset of labor.

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.

Comparison of Direct and Remote Ischaemic Preconditioning of Renal Ischaemia Reperfusion Injury in Rats

Objective

One of the methods that can be used to prevent ischaemia reperfusion (IR) injury is ischaemic preconditioning. The aim of this study was to evaluate and compare the effects of remote and direct ischaemic preconditioning (RIPC and DIPC) histopathologically in the rat renal IR injury model.

Methods

After obtaining an approval from the Dokuz Eylül University School of Medicine Ethics Committee, 28 Wistar Albino male rats were divided into four groups. In Group I (Sham, n=7), laparotomy and left renal pedicle dissection were performed, but nothing else was done. In Group II (IR, n=7), after 45 minutes of left renal pedicle occlusion, reperfusion lasting 4 hours was performed. In Group III (DIPC+IR, n=7), after four cycles of ischaemic preconditioning applied to the left kidney, renal IR was performed. In Group IV (RIPC+IR, n=7), after three cycles of ischaemic preconditioning applied to the left hind leg, renal IR was performed. All rats were sacrificed, and the left kidney was processed for conventional histopathology.

Results

The histopathological injury score of the kidney was significantly lower in the sham group compared with the other groups (p<0.01). The injury scores of the DIPC+IR and RIPC+IR groups were significantly lower than in the IR group (p<0.05). In the RIPC+IR group, the injury score for erythrocyte extravasation was found to be significantly lower than in the DIPC+IR group (p<0.05).

Conclusion

In the present study, it was demonstrated that both DIPC and RIPC decreased renal IR injury, but RIPC was found to be more effective than DIPC. This protective effect requiresfurther detailed experimental and clinical studies.

The effect of remote ischemic preconditioning on serum creatinine in patients undergoing partial nephrectomy: a study protocol for a randomized controlled trial

Background

Acute kidney injury (AKI) may develop during partial nephrectomy due to ischemic reperfusion injury induced by renal artery clamping or surgical insult. The effect of remote ischemic preconditioning (RIPC) on reducing the renal injury after partial nephrectomy has not been evaluated in terms of urinary biomarkers.

Methods/design

We will conduct a randomized controlled trial enrolling the patients who will undergo partial nephrectomy. In the study group, RIPC which consisted of four 5-min cycles of limb ischemia and reperfusion will be conducted after induction of anesthesia. Postoperative serum creatinine values, the incidence of AKI, and urinary biomarkers, including urinary creatinine, microalbumin, β-2 microglobulin, and N-acetyl-beta-D-glucosaminidase, will be compared between groups during the postoperative 2 weeks. Regional oxygen saturation on the skin of the contralateral kidney will be measured to evaluate the association between intraoperative regional oxygen saturation values and renal injury of the operating side.

Discussion

We expect that our trial may demonstrate the effect of RIPC on mitigating the immediate postoperative renal injury and improving patient outcomes after partial nephrectomy. Moreover, our patients will undergo ^99mTc-DTPA radionuclide scintigraphy to calculate glomerular filtration rate 6 and 12 months after surgery. This data should show the long-term effect of RIPC.

Trial registration

ClinicalTrials.gov, ID: NCT03273751. Registered on 6 September 2017.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2820-3) contains supplementary material, which is available to authorized users.

Remote ischemic conditioning: a promising therapeutic intervention for multi-organ protection

Despite decades of formidable exploration, multi-organ ischemia-reperfusion injury (IRI) encountered, particularly amongst elderly patients with clinical scenarios, such as age-related arteriosclerotic vascular disease, heart surgery and organ transplantation, is still an unsettled conundrum that besets clinicians. Remote ischemic conditioning (RIC), delivered via transient, repetitive noninvasive IR interventions to distant organs or tissues, is regarded as an innovative approach against IRI. Based on the available evidence, RIC holds the potential of affording protection to multiple organs or tissues, which include not only the heart and brain, but also others that are likely susceptible to IRI, such as the kidney, lung, liver and skin. Neuronal and humoral signaling pathways appear to play requisite roles in the mechanisms of RIC-related beneficial effects, and these pathways also display inseparable interactions with each other. So far, several hurdles lying ahead of clinical translation that remain to be settled, such as establishment of biomarkers, modification of RIC regimen, and deep understanding of underlying minutiae through which RIC exerts its powerful function. As this approach has garnered an increasing interest, herein, we aim to encapsulate an overview of the basic concept and postulated protective mechanisms of RIC, highlight the main findings from proof-of-concept clinical studies in various clinical scenarios, and also to discuss potential obstacles that remain to be conquered. More well designed and comprehensive experimental work or clinical trials are warranted in future research to confirm whether RIC could be utilized as a non-invasive, inexpensive and efficient adjunct therapeutic intervention method for multi-organ protection.

Current Modalities and Mechanisms Underlying Cardioprotection by Ischemic Conditioning

Ischemic preconditioning is a process which serves to mitigate reperfusion injury. Preconditioning of the heart can be achieved through natural, pharmacological, and mechanical means. Mechanical preconditioning appears to have the greatest chance of good outcomes while methods employing pharmacologic preconditioning have been largely unsuccessful. Remote ischemic preconditioning achieves a cardioprotective effect by applying cycles of ischemia and reperfusion in a distal limb, stimulating the release of a neurohumoral cardioprotective factor incited by stimulation of afferent neurons. The cardioprotective factor stimulates the reperfusion injury salvage kinase (RISK) and survivor activator factor enhancement (SAFE) signaling cascades in cardiomyocytes which promote cell survival by the expression of anti-apoptotic genes and inhibition of the opening of mitochondrial permeability transition pores. Clinical application of ischemic preconditioning involving targets in the RISK and SAFE signaling appears promising in the treatment of acute myocardial infarction; however, clinical trials have yet to demonstrate additional benefit to current therapy.

The effects of remote ischaemic preconditioning on coronary artery function in patients with stable coronary artery disease

Background

Remote ischaemic preconditioning (RIPC) is a cardioprotective intervention invoking intermittent periods of ischaemia in a tissue or organ remote from the heart. The mechanisms of this effect are incompletely understood. We hypothesised that RIPC might enhance coronary vasodilatation by an endothelium-dependent mechanism.

Methods

We performed a prospective, randomised, sham-controlled, blinded clinical trial. Patients with stable coronary artery disease (CAD) undergoing elective invasive management were prospectively enrolled, and randomised to RIPC or sham (1:1) prior to angiography. Endothelial-dependent vasodilator function was assessed in a non-target coronary artery with intracoronary infusion of incremental acetylcholine doses (10^− 6, 10^− 5, 10^− 4 mol/l). Venous blood was sampled pre- and post-RIPC or sham, and analysed for circulating markers of endothelial function. Coronary luminal diameter was assessed by quantitative coronary angiography. The primary outcome was the between-group difference in the mean percentage change in coronary luminal diameter following the maximal acetylcholine dose (Clinicaltrials.gov identifier: NCT02666235).

Results

75 patients were enrolled. Following angiography, 60 patients (mean ± SD age 57.5 ± 8.5 years; 80% male) were eligible and completed the protocol (n = 30 RIPC, n = 30 sham). The mean percentage change in coronary luminal diameter was − 13.3 ± 22.3% and − 2.0 ± 17.2% in the sham and RIPC groups respectively (difference 11.32%, 95%CI: 1.2– 21.4, p = 0.032). This remained significant when age and sex were included as covariates (difference 11.01%, 95%CI: 1.01– 21.0, p = 0.035). There were no between-group differences in endothelial-independent vasodilation, ECG parameters or circulating markers of endothelial function.

Conclusions

RIPC attenuates the extent of vasoconstriction induced by intracoronary acetylcholine infusion. This endothelium-dependent mechanism may contribute to the cardioprotective effects of RIPC.

Mitochondria "THE" target of myocardial conditioning

Several interventions, such as ischemic preconditioning, remote pre/perconditioning, or postconditioning, are known to decrease lethal myocardial ischemia-reperfusion injury. While several signal transduction pathways become activated by such maneuvers, they all have a common end point, namely, the mitochondria. These organelles represent an essential target of the cardioprotective strategies, and the preservation of mitochondrial function is central for the reduction of ischemia-reperfusion injury. In the present review, we address the role of mitochondria in the different conditioning strategies; in particular, we focus on alterations of mitochondrial function in terms of energy production, formation of reactive oxygen species, opening of the mitochondrial permeability transition pore, and mitochondrial dynamics induced by ischemia-reperfusion.

Remote ischaemic conditioning for preventing and treating ischaemic stroke

BACKGROUND

Remote ischaemic conditioning (RIC) has been developed as a neuroprotective strategy to prevent and treat ischaemic stroke. It usually involves restricting blood flow to limbs and then releasing the ischaemic blood to promote a neuroprotective effect. Preclinical studies have suggested that RIC may have beneficial effects in ischaemic stroke patients and those at risk of ischaemic stroke. However, existing evidence is insufficient to demonstrate the efficacy and safety of RIC in preventing and treating ischaemic stroke.

OBJECTIVES

To assess the benefits and harms of RIC for preventing ischaemic stroke and for treating people with ischaemic stroke and those at risk for ischaemic stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (16 January 2018), the Cochrane Central Register of Controlled Trials (CENTRAL; 2017, Issue 12) in the Cochrane Library (January 2018), MEDLINE Ovid (1946 to January 2018), Embase Ovid (1974 to January 2018), Web of Science Core Collection (1950 to January 2018) and three Chinese databases (January 2018). We also searched four ongoing trials registers, reference lists, and conference proceedings.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing RIC with sham RIC or medical management in people with ischaemic stroke or at risk of ischaemic stroke.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, assessed trial quality and risk of bias, and extracted data. We used the GRADE approach to assess the quality of the evidence.

MAIN RESULTS

We included seven trials, involving 735 participants, in this review. We analysed the effects of RIC on preventing and treating ischaemic stroke respectively.We evaluated risk of bias and judged it to be low for generation of allocation sequence in six studies and unclear in one study; unclear for allocation concealment in four studies and low in three studies; high for incomplete outcome data (attrition bias) in five studies and low in two studies; high for blinding in three studies and low in four studies; low for selective reporting; and high for other sources of bias in six studies and low in one study.We included three trials (involving 371 participants) in the analysis of the effects of RIC on ischaemic stroke prevention. In people with symptomatic intracerebral artery stenosis, recurrent stroke was significantly reduced by RIC (risk ratio (RR) 0.32, 95% confidence interval (CI) 0.12 to 0.83; 2 trials, 182 participants, low-quality evidence). In people with carotid stenosis undergoing carotid stenting, there was no significant difference in the incidence of ischaemic stroke between participants treated with RIC and non-RIC (RR 0.22, 95% CI 0.01 to 4.03; 1 trial, 189 participants, low-quality evidence); however the stroke severity (assessed by infarct volume) was significantly lower in participants treated with RIC (mean difference (MD) -0.17 mL, 95% CI -0.23 to -0.11; 1 trial, 189 participants, low-quality evidence). Adverse events associated with RIC were significantly higher in participants treated with RIC (RR 10.91; 95% CI 2.01 to 59.28; 3 trials, 371 participants, low-quality evidence), but no severe adverse event was attributable to RIC treatment. No participants experienced death or cardiovascular events during the period of the studies; and no trial reported haemorrhagic stroke or improvement in neurological, phycological or cognitive impairment.We included four trials (involving 364 participants) in the analysis of the effects of RIC on ischaemic stroke treatment. In acute ischaemic stroke, for people receiving intravenous thrombolysis, the rate of death or dependency was significantly increased by RIC treatment compared with non-RIC treatment (RR 2.34; 95% 1.19 to 4.61; 1 trial, 285 participants, low-quality evidence). In people with acute ischaemic stroke, there was no significant difference between RIC and non-RIC for reducing stroke severity as assessed by the National Institutes of Health Stroke Scale score and the final infarct volume (standardised mean difference (SMD) -0.24 mL, 95% CI -1.02 to 0.54; 2 trials, 175 participants, very low quality evidence). There was no significant difference between RIC and non-RIC for improving the psychological impairment (SMD -0.37 points, 95% CI -1.15 to 0.41; 1 trial, 26 participants, very low quality evidence) and the cognitive impairment (SMD -0.26 points; 95% CI -0.72 to 0.21; 3 trials, 79 participants, low-quality evidence) in people with acute ischaemic stroke and cerebral small vessel disease. No trial reported ischaemic stroke, recurrent ischaemic stroke, improvement in neurological impairment, hemorrhagic stroke, cardiovascular events, and RIC associated adverse events.

AUTHORS' CONCLUSIONS

We found low-quality evidence that RIC may reduce the risk of recurrent stroke in participants with intracerebral artery stenosis and reduce stroke severity in participants undergoing carotid stenting, but it may increase death or dependence in participants with acute ischaemic stroke who are undergoing intravenous thrombolysis. However, there is considerable uncertainty about these conclusions because of the small number of studies and low quality of the evidence.

Mechanical Unloading in Heart Failure

Myocardial injury induces significant changes in ventricular structure and function at both the cellular and anatomic level, leading to ventricular remodeling and subsequent heart failure. Unloading left ventricular pressure has been studied in both the short-term and long-term settings, as a means of preventing or reversing cardiac remodeling. In acute myocardial infarction, cardiac unloading is used to reduce oxygen demand and limit infarct size. Research has demonstrated the benefits of short-term unloading with mechanical circulatory support devices before reperfusion in the context of acute myocardial infarction with cardiogenic shock, and a confirmatory trial is ongoing. In chronic heart failure, ventricular unloading using mechanical circulatory support can reverse many of the cellular and anatomic changes that accompany ventricular remodeling. Ongoing research is evaluating the ability of left ventricular assist devices to promote myocardial recovery and remission from clinical heart failure.

Enhancing and Extending Biological Performance and Resilience

Human performance, endurance, and resilience have biological limits that are genetically and epigenetically predetermined but perhaps not yet optimized. There are few systematic, rigorous studies on how to raise these limits and reach the true maxima. Achieving this goal might accelerate translation of the theoretical concepts of conditioning, hormesis, and stress adaptation into technological advancements. In 2017, an Air Force-sponsored conference was held at the University of Massachusetts for discipline experts to display data showing that the amplitude and duration of biological performance might be magnified and to discuss whether there might be harmful consequences of exceeding typical maxima. The charge of the workshop was "to examine and discuss and, if possible, recommend approaches to control and exploit endogenous defense mechanisms to enhance the structure and function of biological tissues." The goal of this white paper is to fulfill and extend this workshop charge. First, a few of the established methods to exploit endogenous defense mechanisms are described, based on workshop presentations. Next, the white paper accomplishes the following goals to provide: (1) synthesis and critical analysis of concepts across some of the published work on endogenous defenses, (2) generation of new ideas on augmenting biological performance and resilience, and (3) specific recommendations for researchers to not only examine a wider range of stimulus doses but to also systematically modify the temporal dimension in stimulus inputs (timing, number, frequency, and duration of exposures) and in measurement outputs (interval until assay end point, and lifespan). Thus, a path forward is proposed for researchers hoping to optimize protocols that support human health and longevity, whether in civilians, soldiers, athletes, or the elderly patients. The long-term goal of these specific recommendations is to accelerate the discovery of practical methods to conquer what were once considered intractable constraints on performance maxima.

Remote ischemic preconditioning for cardioprotection in elective inpatient abdominal surgery - a randomized controlled trial

Background

Perioperative myocardial injury (PMI) is common in elective inpatient abdominal surgery and correlates with mortality risk. Simple measures for reducing PMI in this cohort are needed. This study evaluated whether remote ischemic preconditioning (RIPC) could reduce PMI in elective inpatient abdominal surgery.

Methods

This was a double-blind, sham-controlled trial with 1:1 parallel randomization. PMI was defined as any post-operative serum troponin T (hs-TNT) > 14 ng/L. Eighty-four participants were randomized to receiving RIPC (5 min of upper arm ischemia followed by 5 min reperfusion, for three cycles) or a sham-treatment immediately prior to surgery. The primary outcome was mean peak post-operative troponin in patients with PMI, and secondary outcomes included mean hs-TnT at individual timepoints, post-operative hs-TnT area under the curve (AUC), cardiovascular events and mortality. Predictors of PMI were also collected. Follow up was to 1 year.

Results

PMI was observed in 21% of participants. RIPC did not significantly influence the mean peak post-operative hs-TnT concentration in these patients (RIPC 25.65 ng/L [SD 9.33], sham-RIPC 23.91 [SD 13.2], mean difference 1.73 ng/L, 95% confidence interval − 9.7 to 13.1 ng/L, P = 0.753). The treatment did not influence any secondary outcome with the pre-determined definition of PMI. Redefining PMI as > 5 ng/L in line with recent data revealed a non-significant lower incidence in the RIPC cohort (68% vs 81%, P = 0.211), and significantly lower early hs-TnT release (12 h time-point, RIPC 5.5 ng/L [SD 5.5] vs sham 9.1 ng/L [SD 8.2], P = 0.03).

Conclusions

RIPC did not at reduce the incidence or severity of PMI in these general surgical patients using pre-determined definitions. PMI is nonetheless common and effective cardioprotective strategies are required.

Trial registration

This trial was registered with Clinicaltrials.gov, NCT01850927, 5th July 2013.

Electronic supplementary material

The online version of this article (10.1186/s12871-018-0524-6) contains supplementary material, which is available to authorized users.

Quantitative impact analysis of remote ischemic conditioning and capsaicin application on human skin microcirculation

BACKGROUND

Improvement of skin microcirculation would be beneficial in transplanted tissues and thus, there is a demand for effective, reliable and harmless angiogenic treatments. The aim of this study was to assess the effect of capsaicin application (CA), the remote effect of capsaicin application (REC), the impact of remote ischemic conditioning (RIC), and the impact of combined remote ischemic conditioning with capsaicin application (Comb) on human skin microcirculation.

METHODS

Perfusion changes were assessed using a laser Doppler device (easyLDI, Aimago Lausanne). 30 healthy volunteers were enrolled and divided into two groups: 1) CA and REC: perfusion was assessed on both forearms after application of capsaicin cream on one forearm with an exposure time of 40 minutes. 2) RIC and Comb: perfusion of one forearm was assessed after four cycles of 5 min blood occlusion and 5 min reperfusion using a tourniquet on the contralateral upper arm and application of capsaicin on the ipsilateral forearm. Baseline skin perfusion measurements of both forearms were carried out initially and were used as intra-individual reference.

RESULTS

1) Skin perfusion significantly increased after capsaicin application (CA = +328.3% , p > 0.05). There was no remote skin perfusion change due to capsaicin (REC). 2) RIC significantly improves skin perfusion (RIC = +20.0% , p < 0.05). The combination of RIC and CA does not improve skin perfusion compared to CA alone (Comb).

CONCLUSIONS

The conditioning techniques RIC and CA showed a significant increase in human skin perfusion, CA being superior to RIC. However, the combination of CA and RIC showed no additional improvement potential as compared to CA alone. Furthermore, a remote effect of capsaicin application could not be demonstrated. These results encourage to analyze if the conditioning treatments are also beneficial for transplanted tissue survival.

Protecting the heart from ischemia/reperfusion injury: an update on remote ischemic preconditioning and postconditioning

PURPOSE OF REVIEW

The most effective strategy for reducing acute myocardial ischemic injury is timely and effective reperfusion. However, myocardial reperfusion can induce further cardiomyocyte death (reperfusion injury). Interventions that protect the heart from ischemia/reperfusion injury, reducing infarct size, can involve remote ischemic preconditioning and postconditioning. These interventions have a promising potential clinical application, and have been the focus of recent research. In this review, we provide an update of remote ischemic preconditioning and postconditioning mechanisms.

RECENT FINDINGS

Remote ischemic preconditioning cardioprotection can occur via a humoral pathway and/or a neural pathway. These two pathways have been described as mechanistically different, but it has been suggested that they could be interdependent. However, remote ischemic postconditioning mainly involves the humoral pathway. In this review, we will discuss the different pathways and mechanisms involved in remote ischemic preconditioning and postconditioning.

SUMMARY

Remote ischemic preconditioning and postconditioning is possible to perform in a clinical setting by intermittent ischemia of an upper or lower limb. Furthermore, clinical trials using this procedure in the context of predictable ischemia-reperfusion have produced promising results, and other studies to define the potential clinical use of these strategies are ongoing.

Neural mechanisms in remote ischaemic conditioning in the heart and brain: mechanistic and translational aspects

Remote ischaemic conditioning (RIC) is a promising method of cardioprotection, with numerous clinical studies having demonstrated its ability to reduce myocardial infarct size and improve prognosis. On the other hand, there are several clinical trials, in particular those conducted in the setting of elective cardiac surgery, that have failed to show any benefit of RIC. These contradictory data indicate that there is insufficient understanding of the mechanisms underlying RIC. RIC is now known to signal indiscriminately, protecting not only the heart, but also other organs. In particular, experimental studies have demonstrated that it is able to reduce infarct size in an acute ischaemic stroke model. However, the mechanisms underlying RIC-induced neuroprotection are even less well understood than for cardioprotection. The existence of bidirectional feedback interactions between the heart and the brain suggests that the mechanisms of RIC-induced neuroprotection and cardioprotection should be studied as a whole. This review, therefore, addresses the topic of the neural component of the RIC mechanism.

Mitochondria and cardiovascular diseases-from pathophysiology to treatment

Mitochondria are the source of cellular energy production and are present in different types of cells. However, their function is especially important for the heart due to the high demands in energy which is achieved through oxidative phosphorylation. Mitochondria form large networks which regulate metabolism and the optimal function is achieved through the balance between mitochondrial fusion and mitochondrial fission. Moreover, mitochondrial function is upon quality control via the process of mitophagy which removes the damaged organelles. Mitochondrial dysfunction is associated with the development of numerous cardiac diseases such as atherosclerosis, ischemia-reperfusion (I/R) injury, hypertension, diabetes, cardiac hypertrophy and heart failure (HF), due to the uncontrolled production of reactive oxygen species (ROS). Therefore, early control of mitochondrial dysfunction is a crucial step in the therapy of cardiac diseases. A number of anti-oxidant molecules and medications have been used but the results are inconsistent among the studies. Eventually, the aim of future research is to design molecules which selectively target mitochondrial dysfunction and restore the capacity of cellular anti-oxidant enzymes.

Remote limb ischemic postconditioning promotes motor function recovery in a rat model of ischemic stroke via the up-regulation of endogenous tissue kallikrein

AIMS

Remote ischemic conditionings, such as pre- and per-conditioning, are known to provide cardioprotection in animal models of ischemia. However, little is known about the neuroprotection effect of postconditioning after cerebral ischemia. In this study, we aim to evaluate the motor function rescuing effect of remote limb ischemic postconditioning (RIPostC) in a rat model of acute cerebral stroke.

METHODS

Left middle cerebral artery occlusion (MCAO) was performed to generate the rat model of ischemic stroke, followed by daily RIPostC treatment for maximum 21 days. The motor function after RIPostC was assessed with foot fault test and balance beam test. Local infarct volume was measured through MRI scanning. Neuronal status was evaluated with Nissl's, HE, and MAP2 immunostaining. Lectin immunostaining was performed to evaluate the microvessel density and area.

RESULTS

Daily RIPostC for more than 21 days promoted motor function recovery and provided long-lasting neuroprotection after MCAO. Reduced infarct volume, rescued neuronal loss, and enhanced microvessel density and size in the injured areas were observed. In addition, the RIPostC effect was associated with the up-regulation of endogenous tissue kallikrein (TK) level in circulating blood and local ischemic brain regions. A TK receptor antagonist HOE-140 partially reversed RIPostC-induced improvements, indicating the specificity of endogenous TK mediating the neuroprotection effect of RIPostC.

CONCLUSION

Our study demonstrates RIPostC treatment as an effective rehabilitation therapy to provide motor function recovery and alleviate brain impairment in a rat model of acute cerebral ischemia. We also for the first time provide evidence showing that the up-regulation of endogenous TK from remote conditioning regions underlies the observed effects of RIPostC.

Remote ischemic preconditioning in myocardial protection in hemodialysis patients

Background

Remote ischemic preconditioning (RIPC) is a procedure that generates a brief period of ischemia followed by reperfusion. The role of RIPC in protecting myocardial ischemia during hemodialysis is not yet established. The aim of the study was to evaluate RIPC myocardial protection as evaluated by ultrasensitive I troponin in hemodialysis outpatients.

Patients and methods

A double-blind randomized trial with two groups: intervention submitted to RIPC and control group without RIPC. Intervention group received RIPC in three consecutive hemodialysis sessions. Blood samples were taken before and after each session. Blood urea nitrogen for calculation of single-pool Kt/v and ultrasensitive I troponin were measured to evaluate dialysis adequacy and myocardial injury.

Results

A total of 47 patients were randomized. About 60.8% were men and 54% were diabetic. The mean single-pool Kt/v was 1.51 in the intervention group and 1.49 in control. The ultrasensitive troponin I measured no significant change from the time of collection: before or after dialysis.

Conclusion

The RIPC applied in three consecutive sessions did not demonstrate superiority to control, therefore another study tested RIPC in 12 consecutive sessions with a positive result in myocardial protection. In our study, more than half of the patients were diabetic. Diabetic patients have a trend to show a lower response to RIPC because of the greater presence of collateral coronary circulation. In summary, in this model there was no interference of RIPC in ultrasensitive troponin I values, but troponin had a high negative predictive value for myocardial infarction in all tested models.

Remote ischemic preconditioning STAT3-dependently ameliorates pulmonary ischemia/reperfusion injury

The lungs are highly susceptible to injury, including ischemia/reperfusion (I/R) injury. Pulmonary I/R injury can occur when correcting conditions such as primary pulmonary hypertension, and is also relatively common after lung transplantation or other cardiothoracic surgery. Methods to reduce pulmonary I/R injury are urgently needed to improve outcomes following procedures such as lung transplantation. Remote liver ischemic preconditioning (RLIPC) is an effective cardioprotective measure, reducing damage caused by subsequent cardiac I/R injury, but little is known about its potential role in pulmonary protection. Here, we analyzed the efficacy and mechanistic basis of RLIPC in a rat model of pulmonary I/R injury. RLIPC reduced lung I/R injury, lessening structural damage, inflammatory cytokine production and apoptosis. In addition, RLIPC preserved pulmonary function compared to controls following lung I/R injury. RLIPC stimulated phosphorylation of pulmonary STAT3, a component of the SAFE signaling pathway, but not phosphorylation of RISK pathway signaling proteins. Accordingly, STAT3 inhibition using AG490 eliminated the pulmonary protection afforded by RLIPC. Our data demonstrate for the first time that RLIPC protects against pulmonary I/R injury, via a signaling pathway requiring STAT3 phosphorylation.

Effects of local versus remote ischemic preconditioning on repeated sprint running performance

BACKGROUND

The aim of this study was to compare the effect of local and remote ischemic preconditioning (IPC) on repeated sprint exercise.

METHODS

Twelve males (age 22±2 years; stature 1.79±0.07 m; body mass 77.8±8.4 kg; mean±SD) completed four trials consisting of remote (arm) and local (leg) IPC and SHAM interventions prior to repeated sprint exercise (3x[6x15+15-m] shuttle sprints), in a double-blind, randomized, crossover designed study. These tests were immediately preceded by IPC (4x5-minute intervals at 220 mmHg bilateral occlusion) or SHAM treatment (4x5-minute intervals at 20 mmHg bilateral occlusion). Sprint performance and percentage decrement score alongside measurement of Tissue Saturation Index, blood lactate and RPE were measured throughout the intervention.

RESULTS

During the IPC/SHAM intervention there was a large decrease in TSI for IPC-arm in comparison to IPC-leg (P<0.05), however IPC-legs resulted in greater soreness compared with the other three conditions (P<0.05). There was no main effects or interaction effects for sprint performance. There was a significant effect of condition (P=0.047, r=0.56) on percentage decrement score across all 18 sprints with IPC demonstrating less fatigue than SHAM. There were no other effects of IPC during the sprint trials for any other physiological measure.

CONCLUSIONS

In conclusion local IPC resulted in more pain/soreness during the IPC/SHAM intervention but both remote and local IPC reduced the fatigue associated with repeated sprint exercise.