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

Remote Ischemic Conditioning in Acute Myocardial Infarction and Shock States

Remote ischemic conditioning is the phenomenon whereby brief, nonlethal episodes of ischemia in one organ (such as a limb) protect a remote organ from ischemic necrosis induced by a longer duration of severe ischemia followed by reperfusion. This phenomenon has been reproduced by dozens of experimental laboratories and was shown to reduce the size of myocardial infarction in many but not all clinical studies. In one recent large clinical trial, remote ischemic conditioning induced by repetitive blood pressure cuff inflations on the arm did not reduce infarct size or improve clinical outcomes. This negative result may have been related in part to the overall success of early reperfusion and current adjunctive therapies, such as antiplatelet therapy, antiremodeling therapies, and low-risk patients, that may make it difficult to show any advantage of newer adjunctive therapies on top of existing therapies. One relevant area in which current outcomes are not as positive as in the treatment of heart attack is the treatment of shock, where mortality rates remain high. Recent experimental studies show that remote ischemic conditioning may improve survival and organ function in shock states, especially hemorrhagic shock and septic shock. In this study, we review the preclinical studies that have explored the potential benefit of this therapy for shock states and describe an ongoing clinical study.

The effect of remote ischaemic preconditioning on myocardial injury in emergency hip fracture surgery (PIXIE trial): phase II randomised clinical trial

OBJECTIVE

To investigate whether remote ischaemic preconditioning (RIPC) prevents myocardial injury in patients undergoing hip fracture surgery.

DESIGN

Phase II, multicentre, randomised, observer blinded, clinical trial.

SETTING

Three Danish university hospitals, 2015-17.

PARTICIPANTS

648 patients with cardiovascular risk factors undergoing hip fracture surgery. 286 patients were assigned to RIPC and 287 were assigned to standard practice (control group).

INTERVENTION

The RIPC procedure was initiated before surgery with a tourniquet applied to the upper arm and consisted of four cycles of forearm ischaemia for five minutes followed by reperfusion for five minutes.

MAIN OUTCOME MEASURES

The original primary outcome was myocardial injury within four days of surgery, defined as a peak plasma cardiac troponin I concentration of 45 ng/L or more caused by ischaemia. The revised primary outcome was myocardial injury within four days of surgery, defined as a peak plasma cardiac troponin I concentration of 45 ng/L or more or high sensitive troponin I greater than 24 ng/L (the primary outcome was changed owing to availability of testing). Secondary outcomes were peak plasma troponin I and total troponin I release during the first four days after surgery (cardiac and high sensitive troponin I), perioperative myocardial infarction, major adverse cardiovascular events, and all cause mortality within 30 days of surgery, length of postoperative stay, and length of stay in the intensive care unit. Several planned secondary outcomes will be reported elsewhere.

RESULTS

573 of the 648 randomised patients were included in the intention-to-treat analysis (mean age 79 (SD 10) years; 399 (70%) women). The primary outcome occurred in 25 of 168 (15%) patients in the RIPC group and 45 of 158 (28%) in the control group (odds ratio 0.44, 95% confidence interval 0.25 to 0.76; P=0.003). The revised primary outcome occurred in 57 of 286 patients (20%) in the RIPC group and 90 of 287 (31%) in the control group (0.55, 0.37 to 0.80; P=0.002). Myocardial infarction occurred in 10 patients (3%) in the RIPC group and 21 patients (7%) in the control group (0.46, 0.21 to 0.99; P=0.04). Statistical power was insufficient to draw firm conclusions on differences between groups for the other clinical secondary outcomes (major adverse cardiovascular events, 30 day all cause mortality, length of postoperative stay, and length of stay in the intensive care unit).

CONCLUSIONS

RIPC reduced the risk of myocardial injury and infarction after emergency hip fracture surgery. It cannot be concluded that RIPC overall prevents major adverse cardiovascular events after surgery. The findings support larger scale clinical trials to assess longer term clinical outcomes and mortality.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02344797.

Myocardial Adaptation in Pseudohypoxia: Signaling and Regulation of mPTP via Mitochondrial Connexin 43 and Cardiolipin

Therapies intended to mitigate cardiovascular complications cannot be applied in practice without detailed knowledge of molecular mechanisms. Mitochondria, as the end-effector of cardioprotection, represent one of the possible therapeutic approaches. The present review provides an overview of factors affecting the regulation processes of mitochondria at the level of mitochondrial permeability transition pores (mPTP) resulting in comprehensive myocardial protection. The regulation of mPTP seems to be an important part of the mechanisms for maintaining the energy equilibrium of the heart under pathological conditions. Mitochondrial connexin 43 is involved in the regulation process by inhibition of mPTP opening. These individual cardioprotective mechanisms can be interconnected in the process of mitochondrial oxidative phosphorylation resulting in the maintenance of adenosine triphosphate (ATP) production. In this context, the degree of mitochondrial membrane fluidity appears to be a key factor in the preservation of ATP synthase rotation required for ATP formation. Moreover, changes in the composition of the cardiolipin’s structure in the mitochondrial membrane can significantly affect the energy system under unfavorable conditions. This review aims to elucidate functional and structural changes of cardiac mitochondria subjected to preconditioning, with an emphasis on signaling pathways leading to mitochondrial energy maintenance during partial oxygen deprivation.

Remote Ischemic Preconditioning Acutely Improves Coronary Microcirculatory Function

Background Remote ischemic preconditioning (RIPC) attenuates myocardial damage during elective and primary percutaneous coronary intervention. Recent studies suggest that coronary microcirculatory function is an important determinant of clinical outcome. The aim of this study was to assess the effect of RIPC on markers of microcirculatory function. Methods and Results Patients referred for cardiac catheterization and fractional flow reserve measurement were randomized to RIPC or sham. Operators and patients were blinded to treatment allocation. Comprehensive physiological assessments were performed before and after RIPC/sham including the index of microcirculatory resistance and coronary flow reserve after intracoronary glyceryl trinitrate and during the infusion of intravenous adenosine. Thirty patients were included (87% male; mean age: 63.1±10.0 years). RIPC and sham groups were similar with respect to baseline characteristics. RIPC decreased the calculated index of microcirculatory resistance (median, before RIPC: 22.6 [interquartile range [IQR]: 17.9-25.6]; after RIPC: 17.5 [IQR: 14.5-21.3]; P=0.007) and increased coronary flow reserve (2.6±0.9 versus 3.8±1.7, P=0.001). These RIPC-mediated changes were associated with a reduction in hyperemic transit time (median: 0.33 [IQR: 0.26-0.40] versus 0.25 [IQR: 0.20-0.30]; P=0.010). RIPC resulted in a significant decrease in the calculated index of microcirculatory resistance compared with sham (relative change with treatment [mean±SD] was -18.1±24.8% versus +6.1±37.5; P=0.047) and a significant increase in coronary flow reserve (+41.2% [IQR: 20.0-61.7] versus -7.8% [IQR: -19.1 to 10.3]; P<0.001). Conclusions The index of microcirculatory resistance and coronary flow reserve are acutely improved by remote ischemic preconditioning. This raises the possibility that RIPC confers cardioprotection during percutaneous coronary intervention as a result of an improvement in coronary microcirculatory function. Clinical Trial Registration URL: www.anzctr.org.au/ . Unique identifier: CTRN12616000486426.

Remote ischemic postconditioning as well as blood plasma from double-conditioned donor ameliorate reperfusion syndrome in skeletal muscle

The aim of this study was to verify the possibility of preparation and effectiveness of the use of blood plasma containing an effector of ischemic tolerance activated by applying two sublethal stresses to a donor. As sublethal stresses, two periods of 20-minute hindlimb ischemia were used with a two-day interval between them. Active plasma was isolated six hours after the second hindlimb ischemia. The effectiveness of active plasma as well as remote postconditioning was tested after three hours of tourniquet-induced ischemia on the gastrocnemius muscle. The wet/dry ratio of gastrocnemius muscle (degree of tissue oedema), nitroblue tetrazolium reduction (tissue necrosis), and CatWalk test (hind limb functionality) were evaluated 24 h after the end of ischemia. Three hours of ischemia increased muscle oedema and necrosis in comparison to control by 26.72% (p < 0.001) and 41.58% (p < 0.001) respectively. Remote ischemic postconditioning as well as injection of conditioned blood plasma significantly prevented these changes, even when they were applied one or three hours after the end of ischemia. Equally effective double-conditioned plasma appears to have better prospects in life-threatening situations such as stroke and myocardial infarction.

Plasma from remotely conditioned pigs reduces infarct size when given before or after ischemia to isolated perfused rat hearts

Short cycles of ischemia/reperfusion in a tissue/organ remote from the heart reduce myocardial ischemia/reperfusion injury. Such remote ischemic conditioning (RIC) can be induced before (pre-), during (per-), or after (post-) the onset of myocardial ischemia. RIC's protection can be transferred with plasma between different individuals, even across species. Infusion of plasma from pigs with remote ischemic per-conditioning(RPERC) reduces infarct size in isolated perfused rat hearts when given before and after the index ischemia. We here determined whether or not infusion of pig plasma is equally protective when given exclusively before or after the index ischemia in isolated perfused rat hearts. Blood was sampled at 10 min reperfusion from Göttingen mini-pigs with 60/180 min coronary occlusion/reperfusion without (placebo, n = 8) or with RPERC (4 × 5 min/5 min hindlimb ischemia/reperfusion, n = 7) starting at 20 min coronary occlusion. Plasma was separated, diluted (1:6), and infused into isolated perfused rat hearts before (plasma_before) or after (plasma_after) 30/120 min global zero-flow ischemia/reperfusion. Infarct size (IS) was demarcated and calculated as percent of ventricular mass (means ± standard deviations). The activation of cardioprotective intracellular signaling cascades was analyzed by Western blot. RPERC-plasma reduced IS (placebo-plasma_before 36 ± 5% and placebo-plasma_after 36 ± 7% versus RPERC-plasma_before 19 ± 3% and RPERC-plasma_after 21 ± 4%; P < 0.001 versus placebo-plasma) and increased the phosphorylation of signal transducer and activator of transcription 3, no matter whether plasma was given before ischemia or during reperfusion. Obviously, the protection, which the released factors exert, is operative during reperfusion. However, pre-ischemic exposure to such cardioprotective factors is remembered throughout ischemia.

Exosomal miR-199a-5p derived from endothelial cells attenuates apoptosis and inflammation in neural cells by inhibiting endoplasmic reticulum stress

Remote ischemic post-conditioning (RIPostC) is a technique that can protect vital organs in an indirect manner, the effects of which are exerted by the long-distance exosome-mediated transfer of functional factors. In the current study, the possible mechanism driving the function of RIPostC was explored using an in vitro system by focusing on miR-199a-5p and its downstream effectors involved in endoplasmic reticulum (ER) stress. Human umbilical vein endothelial cells (HUVECs) were administrated with hypoxia/re-oxygenation (H/R) process and exosomes were collected from the H/R-treated HUVECs. The levels of miR-199a-5p in HUVECs and exosomes were detected. Afterwards, H/R-treated SH-SY5Y neural cells was incubated with H/R HUVEC-derived exosomes, and the effect on cell apoptosis, inflammation, and miR-199a-5p-mediated ER stress was assessed. Furthermore, the key role of miR-199a-5p suppression in the protection effect of HUVEC-derived exosomes was validated by transfecting neural cells with specific inhibitor. The results showed that H/R administration increased miR-199a-5p levels both in HUVECs and exosomes. The incubation of neural cells with exosomes suppressed cell apoptosis and inflammation, and induced the level of miR-199a-5p, which led to suppressed ER stress. Moreover, the transfection of miR-199a-5p inhibitor blocked the anti-H/R function of exosomes. Taken together, the findings outlined in the current study showed that the protection effect of HUVEC derived miR-199a-5p on neural cells was exerted via exosome transfer, which then suppressed the ER stress-induced apoptosis and inflammation by targeting BIP.

Larger infarct size but equal protection by ischemic conditioning in septum and anterior free wall of pigs with LAD occlusion

The ischemic area at risk (AAR) is one major determinant of infarct size (IS). In patients, the largest AAR is seen with a proximal occlusion of the left anterior descending (LAD) coronary artery, which serves parts of the septum and of the anterior free wall. It is not clear, whether regional differences in the perfusion territories also impact on IS and the magnitude of cardioprotection by ischemic conditioning. We have retrospectively analyzed 132 experiments in pigs, which have a similar LAD perfusion territory as humans. The LAD was occluded for 60 min with subsequent 180 min reperfusion. Cardioprotection by either local ischemic pre- or postconditioning or remote ischemic pre- or perconditioning was induced in 93 pigs. The AAR was demarcated by blue dye staining, and IS was assessed by triphenyltetrazolium chloride (TTC) staining. Using digital planimetry, the AAR was separated into sections unequivocally located in the septum (AARS ) or the anterior free wall (AARAFW ). Relative IS was calculated for AARS or AARAFW . AARAFW was larger than AARS (51 ± 9% vs. 34 ± 8% of total AAR; mean ± SD, P < 0.001). Regional myocardial blood flow (microspheres) was not different between septum and anterior free wall. IS without ischemic conditioning tended to be larger in AARS than in AARAFW (50 ± 17% vs. 44 ± 19%; % of AARAWF or AARS , respectively; P = 0.075). Also, with robust IS reduction by ischemic conditioning, the difference in relative IS remained (AARS : 27 ± 16%; AARAFW : 21 ± 16%; P = 0.01). There is a somewhat greater susceptibility for infarction in septal than anterior free wall myocardium. However, ischemic conditioning still reduces IS in both septal and anterior free wall myocardium.

Perioperative Cardioprotection by Remote Ischemic Conditioning

Remote ischemic conditioning has been investigated for cardioprotection to attenuate myocardial ischemia/reperfusion injury. In this review, we provide a comprehensive overview of the current knowledge of the signal transduction pathways of remote ischemic conditioning according to three stages: Remote stimulus from source organ; protective signal transfer through neuronal and humoral factors; and target organ response, including myocardial response and coronary vascular response. The neuronal and humoral factors interact on three levels, including stimulus, systemic, and target levels. Subsequently, we reviewed the clinical studies evaluating the cardioprotective effect of remote ischemic conditioning. While clinical studies of percutaneous coronary intervention showed relatively consistent protective effects, the majority of multicenter studies of cardiac surgery reported neutral results although there have been several promising initial trials. Failure to translate the protective effects of remote ischemic conditioning into cardiac surgery may be due to the multifactorial etiology of myocardial injury, potential confounding factors of patient age, comorbidities including diabetes, concomitant medications, and the coadministered cardioprotective general anesthetic agents. Given the complexity of signal transfer pathways and confounding factors, further studies should evaluate the multitarget strategies with optimal measures of composite outcomes.

A Dual Protective Effect of Intestinal Remote Ischemic Conditioning in a Rat Model of Total Hepatic Ischemia

The present study aimed to investigate the effects of intestinal remote ischemic preconditioning (iRIC) on ischemia-reperfusion injury (IRI) and gut barrier integrity in a rat model of total hepatic ischemia (THI). Male Wistar rats (n = 50; 250–300 g) were randomly allocated into two experimental groups: RIC/Control. Thirty minutes of THI was induced by clamping the hepatoduodenal ligament. iRIC was applied as 4-min of ischemia followed by 11-min of reperfusion by clamping the superior mesenteric artery. Animals were sacrificed at 1, 2, 6, 24 h post-reperfusion (n = 5/group/timepoint). RIC of the gut significantly improved microcirculation of the ileum and the liver. Tissue ATP-levels were higher following iRIC (Liver: 1.34 ± 0.12 vs. 0.97 ± 0.20 μmol/g, p = 0.04) and hepatocellular injury was reduced significantly (ALT: 2409 ± 447 vs. 6613 ± 1117 IU/L, p = 0.003). Systemic- and portal venous IL-6 and TNF-alpha levels were markedly lower following iRIC, demonstrating a reduced inflammatory response. iRIC led to a structural and functional preservation of the intestinal barrier. These results suggest that iRIC might confer a potent protection against the detrimental effects of THI in rats via reducing IRI and systemic inflammatory responses and at the same time by mitigating the dramatic consequences of severe intestinal congestion and bacterial translocation.

Vago-Splenic Axis in Signal Transduction of Remote Ischemic Preconditioning in Pigs and Rats

RATIONALE

The signal transduction of remote ischemic conditioning is still largely unknown.

OBJECTIVE

Characterization of neurohumoral signal transfer and vago-splenic axis in remote ischemic preconditioning (RIPC).

METHODS AND RESULTS

Anesthetized pigs were subjected to 60 minutes of coronary occlusion and 180 minutes of reperfusion (placebo+ischemia/reperfusion [PLA+I/R]). RIPC was induced by 4×5/5 minutes of hindlimb I/R 90 minutes before coronary occlusion (RIPC+I/R). Arterial blood samples were taken after placebo or RIPC before I/R. In subgroups of pigs, bilateral cervical vagotomy, splenectomy, or splenic denervation were performed before PLA+I/R or RIPC+I/R, respectively. In pigs with RIPC+I/R, infarct size (percentage of area at risk) was less than in those with PLA+I/R (23±12% versus 45±8%); splenectomy or splenic denervation abrogated (splenectomy+RIPC+I/R: 38±15%; splenic denervation+RIPC+I/R: 43±5%), and vagotomy attenuated (vagotomy+RIPC+I/R: 36±11%) RIPC protection. RIPC increased phosphorylation of STAT3 (signal transducer and activator of transcription 3) in left ventricular biopsies taken at early reperfusion. Splenectomy or splenic denervation, but not vagotomy, abolished this increased phosphorylation. In rats with vagotomy, splenectomy, or splenic denervation, RIPC (3×5/5 minutes of hindlimb occlusion/reperfusion) or placebo was performed, respectively. Hearts were isolated, saline perfused, and subjected to 30/120-minute global I/R. With RIPC, infarct size (percentage of ventricular mass) was less (20±7%) than with placebo (37±6%), and vagotomy, splenectomy, or splenic denervation abrogated RIPC protection (38±12%, 36±9%, and 36±7%), respectively. Rat spleens were isolated, saline perfused, and splenic effluate (SEff) was sampled after infusion with carbachol (SEff_carbachol) or saline (SEff_saline). Pig plasma or SEff was infused into isolated perfused rat hearts subjected to global I/R. Infarct size was less with infusion of RIPC+I/R_plasma+ (24±6%) than with PLA+I/R_plasma (40±8%), vagotomy+PLA+I/R_plasma (39±11%), splenectomy+PLA+I/R_plasma (35±8%), vagotomy+RIPC+I/R_plasma (40±9%), splenectomy+RIPC+I/R_plasma (33±9%), or splenic denervation+RIPC+I/R_plasma (39±8%), respectively. With infusion of SEff_carbachol, infarct size was less than with infusion of SEff_saline (24 [19-27]% versus 35 [32-38]%).

CONCLUSIONS

Activation of a vago-splenic axis is causally involved in RIPC cardioprotection.

The Role of Heme Oxygenase-1 in Remote Ischemic and Anesthetic Organ Conditioning

The cytoprotective effects of the heme oxygenase (HO) pathway are widely acknowledged. These effects are mainly mediated by degradation of free, pro-oxidant heme and the generation of carbon monoxide (CO) and biliverdin. The underlying mechanisms of protection include anti-oxidant, anti-apoptotic, anti-inflammatory and vasodilatory properties. Upregulation of the inducible isoform HO-1 under stress conditions plays a crucial role in preventing or reducing cell damage. Therefore, modulation of the HO-1 system might provide an efficient strategy for organ protection. Pharmacological agents investigated in the context of organ conditioning include clinically used anesthetics and sedatives. A review from Hoetzel and Schmidt from 2010 nicely summarized the effects of anesthetics on HO-1 expression and their role in disease models. They concluded that HO-1 upregulation by anesthetics might prevent or at least reduce organ injury due to harmful stimuli. Due to its clinical safety, anesthetic conditioning might represent an attractive pharmacological tool for HO-1 modulation in patients. Remote ischemic conditioning (RIC), first described in 1993, represents a similar secure option to induce organ protection, especially in its non-invasive form. The efficacy of RIC has been intensively studied herein, including on patients. Studies on the role of RIC in influencing HO-1 expression to induce organ protection are emerging. In the first part of this review, recently published pre-clinical and clinical studies investigating the effects of anesthetics on HO-1 expression patterns, the underlying signaling pathways mediating modulation and its causative role in organ protection are summarized. The second part of this review sums up the effects of RIC.

Limb Ischemic Conditioning Induces Oxidative Stress Followed by a Correlated Increase of HIF-1α in Healthy Volunteers

BACKGROUND

Local and remote ischemic preconditioning has been used as a protective intervention against ischemia/reperfusion (I/R) damage in several preclinical and clinical studies. However, its physiological mechanisms are not completely known. I/R increases the production of reactive oxygen species, which also serve as messengers for a variety of functions. Hypoxia-inducible factor 1 alpha (HIF-1α) is probably the most important transcription factor mediator of hypoxic signaling.

OBJECTIVE

We hypothesized that limb ischemic conditioning (LIC) induces a local oxidative/nitrosative stress and a correlated increase of HIF-1α plasma levels.

METHODS

An observational, prospective, and single-center study has been conducted in 27 healthy volunteers. LIC was applied: three cycles (5 min of ischemia followed by 5 min of reperfusion) using an ischemia cuff placed on the upper left arm. Time course of 8-isoprostane, nitrite, and HIF-1α levels was measured in blood plasma. Venous blood was sampled from the left arm before tourniquet inflation (basal) and after LIC: 1 min and 2 hr for 8-isoprostane and nitrite; and 1 min, 2 hr, 8 hr, 24 hr, and 48 hr for HIF-1α.

RESULTS

After LIC, we have found an early increase of 8-isoprostane and nitrite. HIF-1α increased at 2 and 8 hr after LIC. We found a direct correlation between HIF-1α and 8-isoprostane and nitrite plasma levels.

CONCLUSIONS

We concluded that LIC induces an early oxidative/nitrosative stress in the arm followed by an increase of HIF-1α plasma levels correlated with 8-isoprostane and nitrite levels, possibly as a local response.

Remote Ischemic Preconditioning Has No Short Term Effect on Blood Pressure, Heart Rate, and Arterial Stiffness in Healthy Young Adults

Objective

Remote ischemic preconditioning (RIPC) are short episodes of ischemia and reperfusion applied to remote tissue to trigger responses in a specific organ or cardiovascular bed. This study investigates whether RIPC has a short-term effect on blood pressure (BP), heart rate, and arterial stiffness.

Patients and Methods

From March 2018 to August 2018, we included 40 healthy volunteers (23 female, age 25.6 ± 2.8 years) into this single-blinded randomized-controlled crossover trial. After measuring BP, heart rate, and arterial stiffness in supine position participants were randomized into intervention or SHAM group. The intervention group then underwent a RIPC protocol (3 cycles of 5 min of 200 mmHg ischemia followed by 5 min reperfusion) at the thigh. The SHAM group followed the same protocol just on the upper arm with 40 mmHg pressure inflation. Directly after this 30-min procedure a reassessment of hemodynamic measures was conducted.

Results

There were no significant changes in all five outcome parameters when comparing the effect of RIPC to SHAM. In peripheral systolic BP the mean difference between groups was Δ1.14 ± 6.5 mmHg (p = 0.672), and for diastolic BP Δ−0.69 ± 4.5 mmHg (p = 0.507). Heart rate shoed a Δ−0.8 ± 4.7 beats/min (p = 0.397). Regarding arterial stiffness measures, there was also no significant improvements thru RIPC. The mean difference between RIPC and SHAM for central systolic BP was Δ0.40 ± 7.2 mmHg (p = 0.951) and for PWV Δ0.01 ± 0.26 m/s (p = 0.563).

Conclusion

This study could not find any short-term effects of RIPC on arterial stiffness, BP, and heart rate in a RCT in young healthy adults.

Effects of remote ischemic conditioning on kidney injury in at-risk patients undergoing elective coronary angiography (PREPARE study): a multicenter, randomized clinical trial

The ability of remote ischemic preconditioning (RIPC) to prevent contrast-induced nephropathy (CIN) following percutaneous coronary angiography in at-risk patients is controversial. No evidence exists regarding potential RIPC positive effects on renal function and clinical outcomes in the long-term. The PREPARE study was a randomized, prospective, multicenter, and double-blinded trial. A total of 222 patients scheduled for coronary angiography and/or percutaneous transluminal coronary angioplasty with an estimated glomerular filtration rate (eGFR) < 40 mL/min/1.73 m², or eGFR between 40 and 60 mL/min/1.73 m² and two further risk factors were allocated to RIPC or control groups. Preventive measures were applied to all patients, including continuous intravenous saline infusion, withdrawal of nephrotoxic drugs, and limited volume of contrast medium. The primary endpoint, namely incidence of CIN, was 3.8% in the control group and 5.1% in the RIPC group (p = 0.74). The secondary endpoints, i.e., changes in serum creatinine and eGFR levels from baseline to 48 hours and from baseline to 12 months following contrast medium exposure, did not differ between both groups. The incidences of all major clinical events at 12 months were similar in both groups. In this population at risk of CIN, preventive strategies were associated with low CIN incidence. RIPC impacted neither the CIN incidence nor both the renal function and clinical outcomes at 1-year follow-up.

Influence of Cardiovascular Risk Factors, Comorbidities, Medication Use and Procedural Variables on Remote Ischemic Conditioning Efficacy in Patients with ST-Segment Elevation Myocardial Infarction

Remote ischemic conditioning (RIC) confers cardioprotection in patients with ST-segment elevation myocardial infarction (STEMI). Despite intense research, the translation of RIC into clinical practice remains a challenge. This may, at least partly, be due to confounding factors that may modify the efficacy of RIC. The present review focuses on cardiovascular risk factors, comorbidities, medication use and procedural variables which may modify the efficacy of RIC in patients with STEMI. Findings of such efficacy modifiers are based on subgroup and post-hoc analyses and thus hold risk of type I and II errors. Although findings from studies evaluating influencing factors are often ambiguous, some but not all studies suggest that smoking, non-statin use, infarct location, area-at-risk of infarction, pre-procedural Thrombolysis in Myocardial Infarction (TIMI) flow, ischemia duration and coronary collateral blood flow to the infarct-related artery may influence on the cardioprotective efficacy of RIC. Results from the on-going CONDI2/ERIC-PPCI trial will determine any clinical implications of RIC in the treatment of patients with STEMI and predefined subgroup analyses will give further insight into influencing factors on the efficacy of RIC.

Involvement of Endothelin-1, H2S and Nrf2 in Beneficial Effects of Remote Ischemic Preconditioning in Global Cerebral Ischemia-Induced Vascular Dementia in Mice

The present study explored the role of endothelin-1, H2S, and Nrf2 in remote preconditioning (RIPC)-induced beneficial effects in ischemia-reperfusion (I/R)-induced vascular dementia. Mice were subjected to 20 min of global ischemia by occluding both carotid arteries to develop vascular dementia, which was assessed using Morris water maze test on 7th day. RIPC was given by subjecting hind limb to four cycles of ischemia (5 min) and reperfusion (5 min) and it significantly restored I/R-induced locomotor impairment, neurological severity score, cerebral infarction, apoptosis markers along with deficits in learning and memory. Biochemically, there was increase in the plasma levels of endothelin-1 along with increase in the brain levels of H2S and its biosynthetic enzymes viz., cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CLS). There was also an increase in the expression of Nrf2 and glutathione reductase in the brain in response to RIPC. Pretreatment with bosentan (dual blocker of ETA and ETB receptors), amino-oxyacetic acid (CBS synthase inhibitor), and DL-propargylglycine (CLS inhibitor) significantly attenuated RIPC-mediated beneficial effects and biochemical alterations. The effects of bosentan on behavioral and biochemical parameters were more significant than individual treatments with CBS or CLS inhibitors. Moreover, CBS and CLS inhibitors did not alter the endothelin-1 levels possibly suggesting that endothelin-1 may act as upstream mediator of H2S. It is concluded that RIPC may stimulate the release endothelin-1, which may activate CBS and CLS to increase the levels of H2S and latter may increase the expression of Nrf2 to decrease oxidative stress and prevent vascular dementia.

Exploring the role and inter-relationship among nitric oxide, opioids, and KATP channels in the signaling pathway underlying remote ischemic preconditioning induced cardioprotection in rats

OBJECTIVES

This study explored the inter-relationship among nitric oxide, opioids, and KATP channels in the signaling pathway underlying remote ischemic preconditioning (RIPC) conferred cardioprotection.

MATERIALS AND METHODS

Blood pressure cuff was placed around the hind limb of the animal and RIPC was performed by 4 cycles of inflation (5 min) followed by deflation (5 min). An ex vivo Langendorff's isolated rat heart model was used to induce ischemia (of 30 min duration)-reperfusion (of 120 min duration) injury.

RESULTS

RIPC significantly decreased ischemia-reperfusion associated injury assessed by decrease in myocardial infarct, LDH and CK release, improvement in postischemic left ventricular function, LVDP, dp/dtmax, and dp/dtmin. Pretreatment with L-NAME and naloxone abolished RIPC-induced cardioprotection. Moreover, preconditioning with sodium nitroprusside (SNP) and morphine produced a cardioprotective effect in a similar manner to RIPC. L-NAME, but not naloxone, attenuated RIPC and SNP preconditioning-induced increase in serum nitrite levels. Morphine preconditioning did not increase the NO levels, probably suggesting that opioids may be the downstream mediators of NO. Furthermore, glibenclamide and naloxone blocked cardioprotection conferred by morphine and SNP, respectively.

CONCLUSION

It may be proposed that the actions of NO, opioids, and KATP channels are interlinked. It is possible to suggest that RIPC may induce the release of NO from endothelium, which may trigger the synthesis of endogenous opioids, which in turn may activate heart localized KATP channels to induce cardioprotection.

An overview of ischemic preconditioning in exercise performance: A systematic review

Ischemic preconditioning (IPC) is an attractive method for athletes owing to its potential to enhance exercise performance. However, the effectiveness of the IPC intervention in the field of sports science remains mitigated. The number of cycles of ischemia and reperfusion, as well as the duration of the cycle, varies from one study to another. Thus, the aim of this systematic review was to provide a comprehensive review examining the IPC literature in sports science. A systematic literature search was performed in PubMed (MEDLINE) (from 1946 to May 2018), Web of Science (sport sciences) (from 1945 to May 2018), and EMBASE (from 1974 to May 2018). We included all studies investigating the effects of IPC on exercise performance in human subjects. To assess scientific evidence for each study, this review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The electronic database search generated 441 potential articles that were screened for eligibility. A total of 52 studies were identified as eligible and valid for this systematic review. The studies included were of high quality, with 48 of the 52 studies having a randomized, controlled trial design. Most studied showed that IPC intervention can be beneficial to exercise performance. However, IPC intervention seems to be more beneficial to healthy subjects who wish to enhance their performance in aerobic exercises than athletes. Thus, this systematic review highlights that a better knowledge of the mechanisms generated by the IPC intervention would make it possible to optimize the protocols according to the characteristics of the subjects with the aim of suggesting to the subjects the best possible experience of IPC intervention.

Early Immunological Effects of Ischemia-Reperfusion Injury: No Modulation by Ischemic Preconditioning in a Randomised Crossover Trial in Healthy Humans

Ischemic preconditioning (IPC) has been protective against ischemia-reperfusion injury (IRI), but the underlying mechanism is poorly understood. We examined whether IPC modulates the early inflammatory response after IRI. Nineteen healthy males participated in a randomised crossover trial with and without IPC before IRI. IPC and IRI were performed by cuff inflation on the forearm. IPC consisted of four cycles of five minutes followed by five minutes of reperfusion. IRI consisted of twenty minutes followed by 15 min of reperfusion. Blood was collected at baseline, 0 min, 85 min and 24 h after IRI. Circulating monocytes, T-cells subsets and dendritic cells together with intracellular activation markers were quantified by flow cytometry. Luminex measured a panel of inflammation-related cytokines in plasma. IRI resulted in dynamic regulations of the measured immune cells and their intracellular activation markers, however IPC did not significantly alter these patterns. Neither IRI nor the IPC protocol significantly affected the levels of inflammatory-related cytokines. In healthy volunteers, it was not possible to detect an effect of the investigated IPC-protocol on early IRI-induced inflammatory responses. This study indicates that protective effects of IPC on IRI is not explained by direct modulation of early inflammatory events.

Editor's Choice- Pathophysiology and therapy of myocardial ischaemia/reperfusion syndrome

There is a need to find interventions able to reduce the extent of injury in reperfused ST-segment elevation myocardial infarction (STEMI) beyond timely reperfusion. In this review, we summarise the clinical impact of STEMI from epidemiological, clinical and biological perspectives. We also revise the pathophysiology underlying the ischaemia/reperfusion syndrome occurring in reperfused STEMI, including the several players involved in this syndrome, such as cardiomyocytes, microcirculation and circulating cells. Interventions aimed to reduce the resultant infarct size, known as cardioprotective therapies, are extensively discussed, putting the focus on both mechanical interventions (i.e. ischaemic conditioning) and promising pharmacological therapies, such as early intravenous metoprolol, exenatide and other glucose modulators, N-acetylcysteine as well as on some other classic therapies which have failed to be translated to the clinical arena. Novel targets for evolving therapeutic interventions to ameliorate ischaemia/reperfusion injury are also discussed. Finally, we highlight the necessity to improve the study design of future randomised clinical trials in the field, as well as to select patients better who can most likely benefit from cardioprotective interventions.

Effect of Ischemic Postconditioning During Primary Percutaneous Coronary Intervention for Patients With ST-Segment Elevation Myocardial Infarction: A Randomized Clinical Trial

Importance

Ischemic postconditioning of the heart during primary percutaneous coronary intervention (PCI) induced by repetitive interruptions of blood flow to the ischemic myocardial region immediately after reopening of the infarct-related artery may limit myocardial damage.

Objective

To determine whether ischemic postconditioning can improve the clinical outcomes in patients with ST-segment elevation myocardial infarction (STEMI).

Design, Setting, And Participants

In this multicenter, randomized clinical trial, patients with onset of symptoms within 12 hours, STEMI, and thrombolysis in myocardial infarction (TIMI) grade 0-1 flow in the infarct-related artery at arrival were randomized to conventional PCI or postconditioning. Inclusion began on March 21, 2011, through February 2, 2014, and follow-up was completed on February 2, 2016. Analysis was based on intention to treat.

Interventions

Patients were randomly allocated 1:1 to conventional primary PCI, including stent implantation, or postconditioning performed as 4 repeated 30-second balloon occlusions followed by 30 seconds of reperfusion immediately after opening of the infarct-related artery and before stent implantation.

Main Outcome and Measures

A combination of all-cause death and hospitalization for heart failure.

Results

During the inclusion period, 1234 patients (975 men [79.0%] and 259 women [21.0%]; mean [SD] age, 62 [11] years) underwent randomization in the trial. Median follow-up was 38 months (interquartile range, 24-58 months). The primary outcome occurred in 69 patients (11.2%) who underwent conventional primary PCI and in 65 (10.5%) who underwent postconditioning (hazard ratio, 0.93; 95% CI, 0.66-1.30; P = .66). The hazard ratios were 0.75 (95% CI, 0.49-1.14; P = .18) for all-cause death and 0.99 (95% CI, 0.60-1.64; P = .96) for heart failure.

Conclusions and Relevance

Routine ischemic postconditioning during primary PCI failed to reduce the composite outcome of death from any cause and hospitalization for heart failure in patients with STEMI and TIMI grade 0-1 flow at arrival.

Trial Registration

clinicaltrials.gov Identifier: NCT01435408.

The coronary circulation in acute myocardial ischaemia/reperfusion injury: a target for cardioprotection

The coronary circulation is both culprit and victim of acute myocardial infarction. The rupture of an epicardial atherosclerotic plaque with superimposed thrombosis causes coronary occlusion, and this occlusion must be removed to induce reperfusion. However, ischaemia and reperfusion cause damage not only in cardiomyocytes but also in the coronary circulation, including microembolization of debris and release of soluble factors from the culprit lesion, impairment of endothelial integrity with subsequently increased permeability and oedema formation, platelet activation and leucocyte adherence, erythrocyte stasis, a shift from vasodilation to vasoconstriction, and ultimately structural damage to the capillaries with eventual no-reflow, microvascular obstruction (MVO), and intramyocardial haemorrhage (IMH). Therefore, the coronary circulation is a valid target for cardioprotection, beyond protection of the cardiomyocyte. Virtually all of the above deleterious endpoints have been demonstrated to be favourably influenced by one or the other mechanical or pharmacological cardioprotective intervention. However, no-reflow is still a serious complication of reperfused myocardial infarction and carries, independently from infarct size, an unfavourable prognosis. MVO and IMH can be diagnosed by modern imaging technologies, but still await an effective therapy. The current review provides an overview of strategies to protect the coronary circulation from acute myocardial ischaemia/reperfusion injury. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

The Effect of Nitric Oxide on Remote Ischemic Preconditioning in Renal Ischemia Reperfusion Injury in Rats

Although remote ischemic preconditioning (RIPC) is an organ-protective maneuver from subsequent ischemia reperfusion injury (IRI) by application of brief ischemia and reperfusion to other organs, its mechanism remains unclear. However, it is known that RIPC reduces the heart, brain, and liver IRI, and that nitric oxide (NO) is involved in the mechanism of this effect. To identify the role of NO in the protective effect of RIPC in renal IRI, this study examined renal function, oxidative status, and histopathological changes using N-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor. Remote ischemic preconditioning was produced by 3 cycles of 5 minutes ischemia and 5 minutes reperfusion. Blood urea nitrogen, creatinine (Cr), and renal tissue malondialdehyde levels were lower, histopathological damage was less severe, and superoxide dismutase level was higher in the RIPC + IRI group than in the IRI group. The renoprotective effect was reversed by L-NAME. Obtained results suggest that RIPC before renal IRI contributes to improvement of renal function, increases antioxidative marker levels, and decreases oxidative stress marker levels and histopathological damage. Moreover, NO is likely to play an important role in this protective effect of RIPC on renal IRI.

Effects of Combined Remote Ischemic Pre-and Post-Conditioning on Neurologic Complications in Moyamoya Disease Patients Undergoing Superficial Temporal Artery-Middle Cerebral Artery Anastomosis

Superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis is the most commonly used treatment for Moyamoya disease. During the perioperative period, however, these patients are vulnerable to ischemic injury or hyperperfusion syndrome. This study investigated the ability of combined remote ischemic pre-conditioning (RIPC) and remote ischemic post-conditioning (RIPostC) to reduce the occurrence of major neurologic complications in Moyamoya patients undergoing STA-MCA anastomosis. The 108 patients were randomly assigned to a RIPC with RIPostC group (n = 54) or a control group (n = 54). Patients in the RIPC with RIPostC group were treated with four cycles of 5-min ischemia and 5-min reperfusion before craniotomy and after STA-MCA anastomosis (RIPostC). The incidence of postoperative neurologic complications and the duration of hospital stay were determined. The overall incidence of neurologic complication was significantly higher in the control group than in the RIPC with RIPostC group (13 vs. 3, p = 0.013). The duration of hospital stay was significantly longer in the control group than in the RIPC with RIPostC group (17.8 (11.3) vs. 13.8 (5.9) days, p = 0.023). Combined remote ischemic pre- and post-conditioning can be effective in reducing neurologic complications and the duration of hospitalization in Moyamoya patients undergoing STA-MCA anastomosis.

Effects of Remote Ischemic Preconditioning in Patients Undergoing Off-Pump Coronary Artery Bypass Graft Surgery

Purpose

This study aimed to evaluate effects of remote ischemic preconditioning (RIPC) on myocardial injury in patients undergoing off-pump coronary artery bypass graft surgery (OPCABG).

Methods

Sixty-five patients scheduled for the OPCABG were randomly assigned to control (n = 32) or RIPC group (n = 33). All patients received general anesthesia. Before the surgical incision, RIPC was induced on an upper limb with repeated 5-min ischemia and 5-min reperfusion for four times. Blood samples were collected from right internal jugular vein. Plasma levels of IL-6, IL-8, IL-10, TNF-α, cTnT, HFABP, IMA, and MDA were detected at pre-operatively and 0, 6, 18, 24, 48, 72, and 120 h after the surgery. Left internal mammary artery (LIMA) and great saphenous vein (GSV) was cut into 2–3 mm for Western blot analysis of Hif-1α.

Results

In the present study, RIPC treatment significantly reduced plasma levels of cardiac troponin T (p < 0.05), heart-type fatty acid binding protein (p < 0.05), ischemia modified albumin (p < 0.05), malondialdehyde (p < 0.05), as well as plasma levels of pro-inflammatory cytokines including IL-6, IL-8, and TNF-α (P < 0.05, respectively). RIPC treatment significantly increased hypoxia-inducible factor-1α (p < 0.05) expression as well. Mechanical ventilation time for postoperative patients was shortened in RIPC group than those in control group (17.4 ± 3.8 h vs. 19.7 ± 2.9 h, respectively, p < 0.05).

Conclusion

RIPC by upper limb ischemia shortens mechanical ventilation time in patients undergoing OPCABG. RIPC treatment reduces postoperative myocardial enzyme expression and pro-inflammatory cytokine production. RIPC is a protective therapeutic approach in the coronary artery bypass graft surgery.

Effect of Remote Ischemic Preconditioning on Complications After Elective Abdominal Aortic Aneurysm Repair: A Meta-Analysis With Randomized Control Trials

OBJECTIVE

This meta-analysis was to evaluate the effect of remote ischemic preconditioning (RIP) on complications after abdominal aortic aneurysm repair.

METHODS

A literature search was conducted in Google scholar, PubMed, Embase, and Web of Science databases up to February 2019. The pooled risk difference (RD) as well as their 95% confidence interval (CI) were calculated by RevMan 5.3 software.

RESULTS

A total of 249 patients receiving abdominal aortic aneurysm repair with RIP and 248 receiving abdominal aortic aneurysm repair without RIP in 7 included studies were reanalyzed in this meta-analysis. The results showed that RIP cannot significantly reduce the postoperative mortality (RD = -0.01, 95% CI: -0.07 to 0.06, P = .87), myocardial infarction (RD = -0.01, 95% CI, -0.09 to 0.07, P = .79), and renal impairment (RD = 0.06, 95% CI: -0.41 to 0.30, P = .89) and renal failure (RD = 0.04, 95% CI: -0.03 to 0.10, P = .30). Moreover, the pooled estimate indicated that the RIP significantly increased the risk of arrhythmia after abdominal aortic aneurysm repair surgery (RD = 0.08, 95% CI: 0.01 to -0.16, P = .03). Nevertheless, sensitivity analyses indicated unreliable results for risk of arrhythmia.

CONCLUSION

There is no evidence that RIP reduces mortality after abdominal aortic aneurysm repair. Moreover, the current evidence is not robust enough to prove the effect of RIP on kidney- and cardiac-related complications.

Mitogen Activated Protein Kinases in Steatotic and Non-Steatotic Livers Submitted to Ischemia-Reperfusion

: We analyzed the participation of mitogen-activated protein kinases (MAPKs), namely p38, JNK and ERK 1/2 in steatotic and non-steatotic livers undergoing ischemia-reperfusion (I-R), an unresolved problem in clinical practice. Hepatic steatosis is a major risk factor in liver surgery because these types of liver tolerate poorly to I-R injury. Also, a further increase in the prevalence of steatosis in liver surgery is to be expected. The possible therapies based on MAPK regulation aimed at reducing hepatic I-R injury will be discussed. Moreover, we reviewed the relevance of MAPK in ischemic preconditioning (PC) and evaluated whether MAPK regulators could mimic its benefits. Clinical studies indicated that this surgical strategy could be appropriate for liver surgery in both steatotic and non-steatotic livers undergoing I-R. The data presented herein suggest that further investigations are required to elucidate more extensively the mechanisms by which these kinases work in hepatic I-R. Also, further researchers based in the development of drugs that regulate MAPKs selectively are required before such approaches can be translated into clinical liver surgery.

Cardioprotective effect of remote ischemic preconditioning with postconditioning on donor hearts in patients undergoing heart transplantation: a single-center, double-blind, randomized controlled trial

Background

The cardioprotective effect of remote ischemic preconditioning (RIPC) in cardiovascular surgery is controversial. This study investigated whether RIPC combined with remote ischemic postconditioning (RIPostC) reduces myocardial injury to donor hearts in patients undergoing heart transplantation.

Methods

One hundred and twenty patients scheduled for orthotopic heart transplantation were enrolled and randomly assigned to an RIPC+RIPostC group (n = 60) or a control (n = 60) group. In the RIPC+RIPostC group, after anesthesia induction, four cycles of 5-min of ischemia and 5-min of reperfusion were applied to the right upper limb by a cuff inflated to 200 mmHg (RIPC) and 20 min after aortic declamping (RIPostC). Serum cardiac troponin I (cTnI) levels were determined preoperatively and at 3, 6, 12, and 24 h after aortic declamping. Postoperative clinical outcomes were recorded. The primary endpoint was a comparison of serum cTnI levels at 6 h after aortic declamping.

Results

Compared with the preoperative baseline, in both groups, serum cTnI levels peaked at 6 h after aortic declamping. Compared with the control group, RIPC+RIPostC significantly reduced serum cTnI levels at 6 h after aortic declamping (38.87 ± 31.81 vs 69.30 ± 34.13 ng/ml, P = 0.02). There were no significant differences in in-hospital morbidity and mortality between the two groups.

Conclusion

In patients undergoing orthotopic heart transplantation, RIPC combined with RIPostC reduced myocardial injury at 6 h after aortic declamping, while we found no evidence of this function provided by RIPC+RIPostC could improve clinical outcomes.

Trial registration

Trial Registration Number: chictr.org.cn. no. ChiCTR-INR-16010234 (prospectively registered). The initial registration date was 9/1/2017.

Attenuation of ST-segment elevation after ischemic conditioning maneuvers reflects cardioprotection online

Ischemic conditioning maneuvers, when induced either locally in the heart or remotely from the heart, reduce infarct size. However, infarct size reduction can be assessed no earlier than hours after established reperfusion. ST-segment elevation and its attenuation might reflect cardioprotection by ischemic conditioning online. Pigs were subjected to regional myocardial ischemia/reperfusion (1 h/3 h). Ischemic conditioning was induced prior to ischemia either locally (preconditioning; IPC; n = 15) or remotely (remote preconditioning; RIPC; n = 21), remotely during ischemia (remote perconditioning; RPER; n = 18), or locally at reperfusion (postconditioning; POCO; n = 9). Pigs without conditioning served as controls (PLA; n = 29). Area at risk and infarct size were measured postmortem, and ST-segment elevation was analyzed in a V2-like electrocardiogram lead. Ischemic conditioning reduced infarct size (PLA 42 ± 11% of area at risk; IPC 18 ± 10%; RIPC 22 ± 12%; RPER 23 ± 12%, POCO 22 ± 11%). With PLA, ST-segment elevation was increased at 5 min ischemia, sustained until 55 min ischemia and further increased at 10 min reperfusion. IPC and RIPC did not impact on ST-segment elevation at 5 min ischemia, but attenuated ST-segment elevation at 55 min ischemia. With RPER, ST-segment elevation was not different from that with PLA at 5 min, but attenuated at 55 min ischemia. POCO abolished the further increase of ST-segment elevation with reperfusion. Cardioprotection by ischemic conditioning is robustly reflected by attenuation of ST-segment elevation online.

Improved Long-term Survival with Remote Limb Ischemic Preconditioning in a Rat Fixed-Pressure Hemorrhagic Shock Model

PURPOSE

We investigated whether bilateral, lower limb remote ischemic preconditioning (RIPC) improved long-term survival using a rat model of hemorrhagic shock/resuscitation.

METHODS

Rats were anesthetized, intubated and ventilated, and randomly assigned to RIPC, induced by inflating bilateral pressure cuffs around the femoral arteries to 200 mmHg for 5 min, followed by 5-min release of the cuffs (repeated for 4 cycles), or control group (cuffs were inflated to 30 mmHg). Hemorrhagic shock was induced by withdrawing blood to a fixed mean blood pressure of 30 mmHg for 30 min, followed by 30 min of resuscitation with shed blood. Rats remained anesthetized for 1 h during which hemodynamics were monitored then they were allowed to survive for 6 weeks.

RESULTS

The percentage of estimated total blood volume withdrawn to maintain a level of 30 mmHg was similar in both groups. RIPC significantly increased survival at 6 weeks: 5 of 27 (19%) rats in the control group and 13 of 26 (50%; p = 0.02) rats in the RIPC group survived. Blood pressure was higher in the RIPC group. The diastolic internal dimension of the left ventricle, an indicator of circulating intravascular blood volume, was significantly larger in the RIPC group at 1 h after initiation of resuscitation compared to the control group (p = 0.04). Left ventricular function assessed by fractional shortening was comparable in both groups at 1 h after initiation of resuscitation. Blood urea nitrogen (BUN) was within normal range in the RIPC group (17.3 ± 1.2 mg/dl) but elevated in the control group (22.0 ± 1.7 mg/dl) at 48 h after shock.

CONCLUSIONS

RIPC significantly improved short-term survival in rats that were subjected to hemorrhagic shock, and this benefit was maintained long term. RIPC led to greater circulating intravascular blood volume in the early phase of resuscitation and improved BUN.

Impact of Anesthetics on Cardioprotection Induced by Pharmacological Preconditioning

Anesthetics, especially propofol, are discussed to influence ischemic preconditioning. We investigated whether cardioprotection by milrinone or levosimendan is influenced by the clinically used anesthetics propofol, sevoflurane or dexmedetomidine. Hearts of male Wistar rats were randomised, placed on a Langendorff system and perfused with Krebs–Henseleit buffer (KHB) at a constant pressure of 80 mmHg. All hearts underwent 33 min of global ischemia and 60 min of reperfusion. Three different anesthetic regimens were conducted throughout the experiments: propofol (11 μM), sevoflurane (2.5 Vol%) and dexmedetomidine (1.5 nM). Under each anesthetic regimen, pharmacological preconditioning was induced by administration of milrinone (1 μM) or levosimendan (0.3 μM) 10 min before ischemia. Infarct size was determined by TTC staining. Infarct sizes in control groups were comparable (KHB-Con: 53 ± 9%, Prop-Con: 56 ± 9%, Sevo-Con: 56 ± 8%, Dex-Con: 53 ± 9%; ns). Propofol completely abolished preconditioning by milrinone and levosimendan (Prop-Mil: 52 ± 8%, Prop-Lev: 52 ± 8%; ns versus Prop-Con), while sevoflurane did not (Sevo-Mil: 31 ± 9%, Sevo-Lev: 33 ± 7%; p < 0.05 versus Sevo-Con). Under dexmedetomidine, results were inconsistent; levosimendan induced infarct size reduction (Dex-Lev: 36 ± 6%; p < 0.05 versus Dex-Con) but not milrinone (Dex-Mil: 51 ± 8%; ns versus Dex-Con). The choice of the anesthetic regimen has an impact on infarct size reduction by pharmacological preconditioning.

Remote Ischemic Preconditioning With the Use of Lower Limb Before Coronary Artery Bypass Surgery With Cardiopulmonary Bypass and Anesthesia With Propofol

OBJECTIVE

to study potantial of remote ischemic preconditioning (RIP) as method of cardioprotection during coronary artery bypass surgery with cardiopulmonary bypass (CPB) and anesthesia with propofol.

MATERIALS AND METHODS

We included in this study 87 patients (7 were excluded) with ischemic heart disease, hospitalized in the clinic of aortic and cardiovascular surgery of the I. M. Sechenov First Moscow State Medical University clinical hospital № 1. All patients had indications for direct myocardial revascularization by coronary artery bypass surgery. One day before operation patients were randomly assigned to 2 groups depending on preparation scheme: main group of RIP and the control group. The frequency of complications during surgery and in the postoperative period was assessed. Troponin I level was measured before, and in 2 and 24 hours after surgery. The level of lactate in the venous blood was measured before and after surgery.

RESULTS

Numbers of intraoperative and early postoperative complications in the main and control groups were similar. There were no differences between groups in troponin I and lactate levels after surgery.

CONCLUSIONS

Remote ischemic preconditioning has no effect on the outcome of coronary artery bypass surgery with cardiopulmonary bypass and anesthesia with propofol.

Acute and chronic remote ischemic conditioning attenuate septic cardiomyopathy, improve cardiac output, protect systemic organs, and improve mortality in a lipopolysaccharide-induced sepsis model

Remote ischemic conditioning (RIC) is acutely cardioprotective in ischemia-reperfusion injury. We aimed to evaluate the effect of RIC on septic cardiomyopathy and associated multi-organ failure in a lipopolysaccharide (LPS)-induced sepsis mouse model. Balb/c mice were divided into sham, LPS, and LPS + RIC groups. LPS 10 mg/kg or saline control was injected intraperitoneally. RIC was performed by four cycles of 5 min ischemia and 5 min reperfusion of the left lower limb just before the LPS injection. Cardiac function on echocardiography, circulating mediators, blood biochemistry, and MAPK signalling was assessed. Survival 7 days after LPS injection was evaluated in sham-treated, RIC, and daily repeated RIC groups. An LPS-induced decrease in cardiac output was ameliorated by RIC with preserved left ventricular systolic function. LPS-induced increases in TNF-α, IL-1β, IL-6, and high-mobility group box 1 protein (HMGB1) were significantly suppressed by RIC. RIC also suppressed increases in plasma cardiac troponin I, aspartate transaminase, alanine transaminase, blood urea nitrogen, and creatinine with suppressed ERK and JNK phosphorylation in heart, liver, and kidney tissue. RIC significantly improved survival rate (p = 0.0037). Survival rate in the daily repeated RIC group was 100%, and it was higher than that in the RIC group (p = 0.0088). In summary, RIC reduced circulating and myocardial inflammatory mediators associated with septic cardiomyopathy, and led to improved ventricular function, cardiac output, and survival. Our data also revealed that chronic RIC has additional benefit in terms of mortality in sepsis. While further studies are required, RIC may be a clinically useful tool to ameliorate sepsis-induced cardiomyopathy.

Clinical significance of chronic myocardial ischemia in coronary artery disease patients

Myocardial ischemia is considered the cornerstone of the treatment of patients with coronary artery disease (CAD). Although the deleterious effects of myocardial infarction, the maximum expression of ischemia, have been extensively studied and described, the clinical effects of chronic, documented myocardial ischemia are not completely clarified. The first studies that compared therapies for coronary disease focused on the presence of anatomical features and assessed ischemia based on the interpretation of the findings of obstructive atherosclerotic lesions. They suggested that revascularization interventions did not confer any clinical advantage over medical therapy (MT), in terms of cardiac or overall death. Other retrospective studies that were dedicated to assessing the impact of documented stress-induced ischemia on cardiovascular outcomes have suggested a prognostic impact of chronic ischemia. However, this has been questioned in recent studies. Moreover, the previous understanding that chronic ischemia could lead to worsening of ventricular function was not confirmed in a recent study. Thus, the prognostic significance of stress-induced ischemia has been questioned. Regarding treatment options, although some previous analyses have suggested that interventional therapies would reduce cardiovascular events in CAD patients with documented ischemia, recent post-hoc studies and metanalysis have shown distinct results. In this review article, the authors discuss myocardial ischemia, the different responses of the myocardium to ischemic insults, ischemic preconditioning, and the main findings of recent studies about the clinical aspects and treatment of patients with chronic, documented myocardial ischemia.

Remote ischemic conditioning in a rat model of testicular torsion: does it offer testicular protection?

BACKGROUND

Testicular torsion is a surgical emergency mainly affecting adolescent boys, with a relatively high rate of missed torsion and testicular loss secondary to delay in prompt diagnosis and surgical intervention. With ischemic reperfusion injury as its underlying culprit, testicular torsion may respond favorably to remote ischemic conditioning (RIC) where a non-privileged site (e.g. limb) is concurrently rendered ischemic to divert the cascade of reperfusion injury from the privileged organ (e.g. testicle), thus offering a protective effect in improving salvage. This mechanism is established for other organs, whereas it has not been evaluated for testis.

AIM

It was aimed to evaluate RIC in a rat model of testicular torsion as a proof of principle that, similar to what has been demonstrated in other organs, RIC does offer testicular protection.

STUDY DESIGN

This is an animal experimental study. Thirty Sprague-Dawley male rats were divided into control group (n = 15) and experimental group (n = 15). Non-survival surgeries of right-sided spermatic cord torsion (720° counter-clockwise twist) were performed for both the groups (45 min) followed by detorsion and reperfusion (5 min) and then orchiectomy. For the experiment group, an intervention of tail clamping to create RIC was applied 5 min after torsion, then unclamping 5 min before detorsion, followed by detorsion and reperfusion for 5 min and then orchiectomy. The testicles were histologically and immunologically examined using a hypoxia inducible factor (HIF-1α) ELISA Kit. The histological findings on ischemic changes, vascular congestion, and immunohistochemistry were quantified using previously described, validated grading systems.

RESULTS

DISCUSSION: This is the first study to demonstrate the concept of RIC in an animal model of testicular torsion. It is limited by the non-availability of similar studies to compare outcomes and by the caution of extrapolating animal studies on humans. It does lay grounds, however, to subsequent studies to further elaborate on this concept and its clinical applicability.

CONCLUSION

When RIC is applied in the experimental setting of testicular torsion, there is less evidence of hypoxic injury by histology and immunohistochemistry.

Remote ischemic preconditioning ameliorates indirect acute lung injury by modulating phosphorylation of IκBα in mice

OBJECTIVE

Acute lung injury is responsible for mortality in seriously ill patients. Previous studies have shown that systemic inflammation is attenuated by remote ischemic preconditioning (RIPC) via reducing nuclear factor-kappa B (NF-κB). Therefore, we investigated whether lipopolysaccharide (LPS)-induced indirect acute lung injury (ALI) can be protected by RIPC.

METHODS

RIPC was accomplished by 10 minutes of occlusion using a tourniquet on the right hind limb of mice, followed by 10 minutes of reperfusion. This process was repeated three times. Intraperitoneal LPS (20 mg/kg) was administered to induce indirect ALI. Inflammatory cytokines in bronchoalveolar lavage fluid were analyzed using an enzyme-linked immunosorbent assay. Pulmonary tissue was excised for histological examination, and for examining NF-κB activity and phosphorylation of inhibitor of κBα (IκBα).

RESULTS

NF-κB activation and LPS-induced histopathological changes in the lungs were significantly alleviated in the RIPC group. RIPC reduced phosphorylation of IκBα in lung tissue of ALI mice.

CONCLUSIONS

RIPC attenuates endotoxin-induced indirect ALI. This attenuation might occur through modification of NF-κB mediation of cytokines by modulating phosphorylation of IκBα.

Diabetes abolish cardioprotective effects of remote ischemic conditioning: evidences and possible mechanisms

Diabetes mellitus significantly hampers the development of cardioprotective response to remote pre/post/perconditioning stimuli by impairing the activation of cardioprotective signaling pathways. Among the different pathways, the impairment in O-linked β-N-acetylglucosamine (O-GlcNAc) signaling and release of cardioprotective humoral factor may contribute in attenuating remote preconditioning-induced cardioprotection. Moreover, the failure to phosphorylate extracellular signal related kinase (ERK), phosphoinositide-3-kinase (PI3K), and AKT along with up-regulation of mechanistic target of rapamycin (mTOR) and decrease in autophagy may also attenuate remote preconditioning-induced cardioprotection. Remote perconditioning stimulus also fails to phosphorylate AKT kinase in diabetic heart. In addition, diabetes may increase the oxidative stress, reactive oxygen species (ROS) production, decrease the beclin expression, and inhibit autophagy to attenuate remote perconditioning-induced cardioprotection. Moreover, diabetes-induced increase in the Rho-associated kinase (ROCK) activity, decrease in the arginase activity, and reduction in nitric oxide (NO) bioavailability may also contribute in decreasing remote perconditioning-induced cardioprotection. Diabetes may reduce the phosphorylation of adenosine 5'-monophosphate activated protein kinase (AMPKα) and increase the phosphorylation of mTOR to attenuate cardioprotection of remote postconditioning. The present review describes the role of diabetes in attenuating remote ischemic conditioning-induced cardioprotection along with the possible mechanisms.

Adenosine A1 receptors and mitochondria: targets of remote ischemic preconditioning

Adenosine is involved in classic preconditioning in most species and acts especially through adenosine A₁ and A₃ receptors. The aim of the present study was to evaluate whether remote ischemic preconditioning (rIPC) activates adenosine A₁ receptors and improves mitochondrial function, thereby reducing myocardial infarct size. Isolated rat hearts were subjected to 30 min of global ischemia and 60 min of reperfusion [ischemia-reperfusion (I/R)]. In a second group, before isolation of the heart, a rIPC protocol (3 cycles of hindlimb I/R) was performed. Infarct size was measured with tetrazolium staining, and Akt/endothelial nitric oxide (NO) synthase (eNOS) expression/phosphorylation and mitochondrial function were evaluated after ischemia at 10 and 60 min of reperfusion. As expected, rIPC significantly decreased infarct size. This beneficial effect was abolished only when 8-cyclopentyl-1,3-dipropylxanthine (adenosine A₁ receptor blocker) and N^G-nitro-l-arginine methyl ester (NO synthesis inhibitor) were administered during the reperfusion phase. At the early reperfusion phase, rIPC induced significant Akt and eNOS phosphorylation, which was abolished by the perfusion with an adenosine A₁ receptor blocker. I/R led to impaired mitochondrial function, which was attenuated by rIPC and mediated by adenosine A₁ receptors. In conclusion, we demonstrated that rIPC limits myocardial infarct by activation of adenosine A₁ receptors at early reperfusion in the isolated rat heart. Interestingly, rIPC appears to reduce myocardial infarct size by the Akt/eNOS pathway and improves mitochondrial function during myocardial reperfusion. NEW & NOTEWORTHY Adenosine is involved in classic preconditioning and acts especially through adenosine A₁ and A₃ receptors. However, its role in the mechanism of remote ischemic preconditioning is controversial. In this study, we demonstrated that remote ischemic preconditioning activates adenosine A₁ receptors during early reperfusion, inducing Akt/endothelial nitric oxide synthase phosphorylation and improving mitochondrial function, thereby reducing myocardial infarct size.

Ischaemic and hypoxic conditioning: potential for protection of vital organs

NEW FINDINGS

What is the topic of this review? Remote ischaemic preconditioning (RIPC) and hypoxic preconditioning as novel therapeutic approaches for cardiac and neuroprotection. What advances does it highlight? There is improved understanding of mechanisms and signalling pathways associated with ischaemic and hypoxic preconditioning, and potential pitfalls with application of these therapies to clinical trials have been identified. Novel adaptations of preconditioning paradigms have also been developed, including intermittent hypoxia training, RIPC training and RIPC-exercise, extending their utility to chronic settings.

ABSTRACT

Myocardial infarction and stroke remain leading causes of death worldwide, despite extensive resources directed towards developing effective treatments. In this Symposium Report we highlight the potential applications of intermittent ischaemic and hypoxic conditioning protocols to combat the deleterious consequences of heart and brain ischaemia. Insights into mechanisms underlying the protective effects of intermittent hypoxia training are discussed, including the activation of hypoxia-inducible factor-1 and Nrf2 transcription factors, synthesis of antioxidant and ATP-generating enzymes, and a shift in microglia from pro- to anti-inflammatory phenotypes. Although there is little argument regarding the efficacy of remote ischaemic preconditioning (RIPC) in pre-clinical models, this strategy has not consistently translated into the clinical arena. This lack of translation may be related to the patient populations targeted thus far, and the anaesthetic regimen used in two of the major RIPC clinical trials. Additionally, we do not fully understand the mechanism through which RIPC protects the vital organs, and co-morbidities (e.g. hypercholesterolemia, diabetes) may interfere with its efficacy. Finally, novel adaptations have been made to extend RIPC to more chronic settings. One adaptation is RIPC-exercise (RIPC-X), an innovative paradigm that applies cyclical RIPC to blood flow restriction exercise (BFRE). Recent findings suggest that this novel exercise modality attenuates the exaggerated haemodynamic responses that may limit the use of conventional BFRE in some clinical settings. Collectively, intermittent ischaemic and hypoxic conditioning paradigms remain an exciting frontier for the protection against ischaemic injuries.