Systemic protection through remote ischemic preconditioning is spread by platelet-dependent signaling in mice

Remote ischemic conditioning in experimental hepatic ischemia‑reperfusion: A systematic review and meta‑analysis

Remote ischemic conditioning (RIC), including pre-conditioning (RIPC, before the ischemic event), per-conditioning (RIPerC, during the ischemic event), and post-conditioning (RIPostC, after the ischemic event), protects the liver in animal hepatic ischemia-reperfusion injuries models. However, several questions regarding the optimal timing of intervention and administration protocols remain unanswered. Therefore, the preclinical evidence on RIC in the HIRI models was systematically reviewed and meta-analyzed in the present review to provide constructive and helpful information for future works. In the present review, 39 articles were identified by searching the PubMed, OVID, Web of Science and Embase databases spanned from database inception to July 2024. According to the preferred reporting items for systematic reviews and meta-analyses guidelines, data were extracted independently by two researchers. The primary outcomes evaluated in this study were those directly related to liver injury, such as alanine transaminase (ALT), aspartate transaminase (AST) and liver histopathology. The risk of bias was assessed using the risk of bias tool of the SYstematic Review Centre for Laboratory animal Experimentation (SYRCLE). The findings were expressed as standardized mean difference (SMD) and analyzed using random-effects models. Egger's test was used to evaluate the publication bias. RIC significantly reduced the changes in ALT, AST and liver histopathology (all P<0.00001). These effects had two peaks, with the first peak of RIPerC/RIPostC occurring earlier, regardless of models and species. RIPerC/RIPostC exerted significant effects on changes in ALT and AST [ALT SMD (95% confidence interval (CI]): RIPC -1.97 (-2.40, -1.55) vs. -2.78 (-3.77, -1.78); P=0.142; AST SMD (95%CI): RIPC -1.45 (-1.90, -0.99) vs. -2.13 (-2.91, -1.34); P=0.142], and RIPC had a greater effect on liver histopathology change [SMD (95%CI): RIPC -2.68 (-3.67, -1.69) vs. -1.58 (-2.24, -0.92); P=0.070]; however, no interactions were observed between the two groups in the meta-regression analysis. RIC is the most effective in experimental HIRI, using a 10-25-min dose. These outcomes suggest that RIC may be a promising strategy for treating HIRI; however, future studies using repeated doses in animal models with comorbidities will present novel ideas for its therapeutic application. The protocol of present study was registered with PROSPERO (CRD42023482725).

Remote ischemic preconditioning versus sham-control for prevention of anastomotic leakage after resection for rectal cancer (RIPAL trial): a pilot randomized controlled, triple-blinded monocenter trial

PURPOSE

Remote ischemic preconditioning (RIPC) reportedly reduces ischemia‒reperfusion injury (IRI) in various organ systems. In addition to tension and technical factors, ischemia is a common cause of anastomotic leakage (AL) after rectal resection. The aim of this pilot study was to investigate the potentially protective effect of RIPC on anastomotic healing and to determine the effect size to facilitate the development of a subsequent confirmatory trial.

MATERIALS AND METHODS

Fifty-four patients with rectal cancer (RC) who underwent anterior resection were enrolled in this prospectively registered (DRKS0001894) pilot randomized controlled triple-blinded monocenter trial at the Department of Surgery, University Medicine Mannheim, Mannheim, Germany, between 10/12/2019 and 19/06/2022. The primary endpoint was AL within 30 days after surgery. The secondary endpoints were perioperative morbidity and mortality, reintervention, hospital stay, readmission and biomarkers of ischemia‒reperfusion injury (vascular endothelial growth factor, VEGF) and cell death (high mobility group box 1 protein, HMGB1). RIPC was induced through three 10-min cycles of alternating ischemia and reperfusion to the upper extremity.

RESULTS

Of the 207 patients assessed, 153 were excluded, leaving 54 patients to be randomized to the RIPC or the sham-RIPC arm (27 each per arm). The mean age was 61 years, and the majority of patients were male (37:17 (68.5:31.5%)). Most of the patients underwent surgery after neoadjuvant therapy (29/54 (53.7%)) for adenocarcinoma (52/54 (96.3%)). The primary endpoint, AL, occurred almost equally frequently in both arms (RIPC arm: 4/25 (16%), sham arm: 4/26 (15.4%), p = 1.000). The secondary outcomes were comparable except for a greater rate of reintervention in the sham arm (9 (6-12) vs. 3 (1-5), p = 0.034). The median duration of endoscopic vacuum therapy was shorter in the RIPC arm (10.5 (10-11) vs. 38 (24-39) days, p = 0.083), although the difference was not statistically significant.

CONCLUSION

A clinically relevant protective effect of RIPC on anastomotic healing after rectal resection cannot be assumed on the basis of these data.

Remote ischemic preconditioning for reduction of ischemia-reperfusion injury after hepatectomy: A randomized sham-controlled trial

BACKGROUND

Remote ischemic preconditioning reduces ischemia-reperfusion injury in patients undergoing hepatectomy. Moreover, there is evidence that the protective effects of remote ischemic preconditioning may be more pronounced in pre-damaged livers. The objective of this trial was to investigate the extent to which remote ischemic preconditioning can attenuate ischemia-reperfusion injury after hepatectomy and Pringle maneuver in patients with chronic liver disease.

METHODS

In this randomized, controlled, triple-blind monocenter trial, a total of 102 patients with chronic liver disease and planned hepatectomy were enrolled between December 2019 and March 2022. Eligible patients were randomized to the remote ischemic preconditioning or sham arms. Remote ischemic preconditioning was induced through 3 10-minute cycles of alternating ischemia and reperfusion of the upper extremity. The study was prospectively registered in the German Clinical Trials Registry (DRKS00018931).

RESULTS

A total of 102 patients were included in the study and were randomized (51 per arm). The median age was 69.5 years, approximately two-thirds of the patients were male (69/102, 67.7%), and the mean body mass index was 25.6 kg/m2. Most patients were classified as American Society of Anesthesiologists II (55/102, 53.9%) or III (45/102, 44.1%). The primary endpoint, the transaminases on the first postoperative day (alanine aminotransferase /aspartate aminotransferase: remote ischemic preconditioning arm: 250 (35-1721)/320 (42-1525) U/L versus sham control arm: 283 (32-792)/356 (20-1851) U/L, P = .820/0.639), clinical outcomes as well as remote ischemic preconditioning biomarker levels were comparable between both arms.

CONCLUSION

Remote ischemic preconditioning did not achieve a significant reduction in postoperative transaminase levels, nor did it affect clinical results and biomarkers.

Platelet-Mediated Transfer of Cardioprotection by Remote Ischemic Conditioning and Its Abrogation by Aspirin But Not by Ticagrelor

PURPOSE

The role of platelets during myocardial ischemia/reperfusion (I/R) is ambivalent. They contribute to injury but also to cardioprotection. Repeated blood flow restriction and reperfusion in a tissue/organ remote from the heart (remote ischemic conditioning, RIC) reduce myocardial I/R injury and attenuate platelet activation. Whether or not platelets mediate RIC's cardioprotective signal is currently unclear.

METHODS AND RESULTS

Venous blood from healthy volunteers (without or with pretreatment of 500/1000 mg aspirin or 180 mg ticagrelor orally, 2-3 h before the study, n = 18 each) was collected before and after RIC (3 × 5 min blood pressure cuff inflation at 200 mmHg on the left upper arm/5 min deflation). Washed platelets were isolated. Platelet-poor plasma was used to prepare plasma-dialysates. Platelets (25 × 103/µL) or plasma-dialysates (1:10) prepared before and after RIC from untreated versus aspirin- or ticagrelor-pretreated volunteers, respectively, were infused into isolated buffer-perfused rat hearts. Hearts were subjected to global 30 min/120 min I/R. Infarct size was stained. Infarct size was less with infusion of platelets/plasma-dialysate after RIC (18 ± 7%/23 ± 9% of ventricular mass) than with platelets/plasma-dialysate before RIC (34 ± 7%/33 ± 8%). Aspirin pretreatment abrogated the transfer of RIC's cardioprotection by platelets (after/before RIC, 34 ± 7%/33 ± 7%) but only attenuated that by plasma-dialysate (after/before RIC, 26 ± 8%/32 ± 5%). Ticagrelor pretreatment induced an in vivo formation of cardioprotective factor(s) per se (platelets/plasma-dialysate before RIC, 26 ± 7%/26 ± 7%) but did not impact on RIC's cardioprotection by platelets/plasma-dialysate (20 ± 7%/21 ± 5%).

CONCLUSION

Platelets serve as carriers for RIC's cardioprotective signal through an aspirin-sensitive and thus cyclooxygenase-dependent mechanism. The P2Y12 inhibitor ticagrelor per se induces a humoral cardioprotective signal.

Machine perfusion of the liver and bioengineering

With the increasing number of accepted candidates on waiting lists worldwide, there is an urgent need to expand the number and the quality of donor livers. Dynamic preservation approaches have demonstrated various benefits, including improving liver function and graft survival, and reducing liver injury and post-transplant complications. Consequently, organ perfusion techniques are being used in clinical practice in many countries. Despite this success, a proportion of livers do not meet current viability tests required for transplantation, even with the use of modern perfusion techniques. Therefore, devices are needed to further optimise machine liver perfusion - one promising option is to prolong machine liver perfusion for several days, with ex situ treatment of perfused livers. For example, stem cells, senolytics, or molecules targeting mitochondria or downstream signalling can be administered during long-term liver perfusion to modulate repair mechanisms and regeneration. Besides, today's perfusion equipment is also designed to enable the use of various liver bioengineering techniques, to develop scaffolds or for their re-cellularisation. Cells or entire livers can also undergo gene modulation to modify animal livers for xenotransplantation, to directly treat injured organs or to repopulate such scaffolds with "repaired" autologous cells. This review first discusses current strategies to improve the quality of donor livers, and secondly reports on bioengineering techniques to design optimised organs during machine perfusion. Current practice, as well as the benefits and challenges associated with these different perfusion strategies are discussed.

Mitochondria and ischemia reperfusion injury

PURPOSE OF REVIEW

This review describes the role of mitochondria in ischemia-reperfusion-injury (IRI).

RECENT FINDINGS

Mitochondria are the power-house of our cells and play a key role for the success of organ transplantation. With their respiratory chain, mitochondria are the main energy producers, to fuel metabolic processes, control cellular signalling and provide electrochemical integrity. The mitochondrial metabolism is however severely disturbed when ischemia occurs. Cellular energy depletes rapidly and various metabolites, including Succinate accumulate. At reperfusion, reactive oxygen species are immediately released from complex-I and initiate the IRI-cascade of inflammation. Prior to the development of novel therapies, the underlying mechanisms should be explored to target the best possible mitochondrial compound. A clinically relevant treatment should recharge energy and reduce Succinate accumulation before organ implantation. While many interventions focus instead on a specific molecule, which may inhibit downstream IRI-inflammation, mitochondrial protection can be directly achieved through hypothermic oxygenated perfusion (HOPE) before transplantation.

SUMMARY

Mitochondria are attractive targets for novel molecules to limit IRI-associated inflammation. Although dynamic preservation techniques could serve as delivery tool for new therapeutic interventions, their own inherent mechanism should not only be studied, but considered as key treatment to reduce mitochondrial injury, as seen with the HOPE-approach.

Mitochondria and Cancer Recurrence after Liver Transplantation-What Is the Benefit of Machine Perfusion?

Tumor recurrence after liver transplantation has been linked to multiple factors, including the recipient's tumor burden, donor factors, and ischemia-reperfusion injury (IRI). The increasing number of livers accepted from extended criteria donors has forced the transplant community to push the development of dynamic perfusion strategies. The reason behind this progress is the urgent need to reduce the clinical consequences of IRI. Two concepts appear most beneficial and include either the avoidance of ischemia, e.g., the replacement of cold storage by machine perfusion, or secondly, an endischemic organ improvement through perfusion in the recipient center prior to implantation. While several concepts, including normothermic perfusion, were found to reduce recipient transaminase levels and early allograft dysfunction, hypothermic oxygenated perfusion also reduced IRI-associated post-transplant complications and costs. With the impact on mitochondrial injury and subsequent less IRI-inflammation, this endischemic perfusion was also found to reduce the recurrence of hepatocellular carcinoma after liver transplantation. Firstly, this article highlights the contributing factors to tumor recurrence, including the surgical and medical tissue trauma and underlying mechanisms of IRI-associated inflammation. Secondly, it focuses on the role of mitochondria and associated interventions to reduce cancer recurrence. Finally, the role of machine perfusion technology as a delivery tool and as an individual treatment is discussed together with the currently available clinical studies.

GC-MS Profile of Hua-Feng-Dan and RNA-Seq Analysis of Induced Adaptive Responses in the Liver

Background: Hua-Feng-Dan is a patent Chinese medicine for stroke recovery and various diseases. This study used GC-MS to profile its ingredients and RNA-Seq to analyze the induced adaptive response in the liver. Methods: Hua-Feng-Dan was subjected to steam distillation and solvent extraction, followed by GC-MS analysis. Mice were orally administered Hua-Feng-Dan and its "Guide drug" Yaomu for 7 days. Liver pathology was examined, and total RNA isolated for RNA-Seq, followed by bioinformatic analysis and quantitative real-time PCR (qPCR). Results: Forty-four volatile and fifty liposoluble components in Hua-Feng-Dan were profiled and analyzed by the NIST library and their concentrations quantified. The major components (>1%) in volatile (5) and liposoluble (10) were highlighted. Hua-Feng-Dan and Yaomu at hepatoprotective doses did not produce liver toxicity as evidenced by histopathology and serum enzyme activities. GO Enrichment revealed that Hua-Feng-Dan affected lipid homeostasis, protein folding, and cell adhesion. KEGG showed activated cholesterol metabolism, bile secretion, and PPAR signaling pathways. Differentially expressed genes (DEGs) were identified by DESeq2 with p < 0.05 compared to controls. Hua-Feng-Dan produced more DEGs than Yaomu. qPCR on selected genes largely verified RNA-Seq results. Ingenuity Pathways Analysis of the upstream regulator revealed activation of MAPK and adaptive responses by Hua-Feng-Dan, and Yaomu was less effective. Hua-Feng-Dan-induced DEGs were highly correlated with the Gene Expression Omnibus database of chemical-induced adaptive transcriptome changes in the liver. Conclusion: GC-MS primarily profiled volatile and liposoluble components in Hua-Feng-Dan. Hua-Feng-Dan at the hepatoprotective dose did not produce liver pathological changes but induced metabolic and signaling pathway activations. The effects of Hua-Feng-Dan on liver transcriptome changes point toward induced adaptive responses to program the liver to produce hepatoprotective effects.

Dualistic role of platelets in living donor liver transplantation: Are they harmful?

Platelets are anucleate fragments mainly involved in hemostasis and thrombosis, and there is emerging evidence that platelets have other nonhemostatic potentials in inflammation, angiogenesis, regeneration and ischemia/reperfusion injury (I/R injury), which are involved in the physiological and pathological processes during living donor liver transplantation (LDLT). LDLT is sometimes associated with impaired regeneration and severe I/R injury, leading to postoperative complications and decreased patient survival. Recent studies have suggested that perioperative thrombocytopenia is associated with poor graft regeneration and postoperative morbidity in the short and long term after LDLT. Although it is not fully understood whether thrombocytopenia is the cause or result, increasing platelet counts are frequently suggested to improve posttransplant outcomes in clinical studies. Based on rodent experiments, previous studies have identified that platelets stimulate liver regeneration after partial hepatectomy. However, the role of platelets in LDLT is controversial, as platelets are supposed to aggravate I/R injury in the liver. Recently, a rat model of partial liver transplantation (LT) was used to demonstrate that thrombopoietin-induced thrombocytosis prior to surgery accelerated graft regeneration and improved the survival rate after transplantation. It was clarified that platelet-derived liver regeneration outweighed the associated risk of I/R injury after partial LT. Clinical strategies to increase perioperative platelet counts, such as thrombopoietin, thrombopoietin receptor agonist and platelet transfusion, may improve graft regeneration and survival after LDLT.

Protective effect of ischemic postconditioning on ischemia reperfusion injury in steatotic rat livers

Background

Hepatic steatosis creates a significant risk of liver resection and transplantation and is extremely susceptible to ischemia/reperfusion (I/R) injury. Ischemic postconditioning (IPostC) has been shown to attenuate I/R injury in normal livers; however, its role in steatotic livers remains unknown. The current study sought to explore whether IPostC could attenuate normothermic I/R injury in rats with steatotic livers and to investigate potential protective measures.

Methods

Hepatic steatosis was triggered in Wistar rats fed high-fat diets. The role of IPostC was detected in normal and steatotic livers with 30 min of ischemia and 6 h of reperfusion. Blood and liver tissues were collected to assess hepatocyte damage, lipid peroxidation, inflammatory factors, neutrophil accumulation, and adenosine triphosphate (ATP) content.

Results

Compared to normal livers, steatotic livers were more susceptible to I/R damage, as evidenced by incremental concentrations of liver enzymes in the blood and more severe pathological changes in the liver. Hepatic I/R injury was significantly reduced by IPostC in both normal and steatotic livers. We further found that endogenous protective measures moderated lipid peroxidation, inflammatory cytokine expression and neutrophil accumulation, and reduced follow-up hepatic injury. The ATP content of steatotic livers was also significantly lower than that of Normal livers before and after I/R injury. IPostC greatly preserved the ATP content of normal and steatotic livers with I/R injury.

Conclusions

IPostC appears to provide important protection against hepatic I/R injury in normal and steatotic livers under normothermic conditions. These data have important clinical implications for liver surgery and transplantation.

Attenuation of peripheral serotonin inhibits tumor growth and enhances immune checkpoint blockade therapy in murine tumor models

[Figure: see text].

Platelets Stimulate Liver Regeneration in a Rat Model of Partial Liver Transplantation

Living donor liver transplantation (LDLT) is sometimes associated with impaired regeneration and severe ischemia/reperfusion injury (IRI) in the graft, resulting in small-for-size syndrome (SFSS). Platelets were previously reported to stimulate liver regeneration in models of hepatectomy, but the evidence in partial liver transplantation (LT) is lacking. In this study, a rat model of partial LT was used, and the impact of thrombopoietin (TPO)-induced perioperative thrombocytosis on graft regeneration, IRI, and survival was investigated. In experiment 1, a 30% partial LT was performed. Under thrombocytosis, SFSS was attenuated, as shown by decreased levels of serum aminotransferases, bilirubin, and ascites. Serum hepatocyte regeneration-related cytokines, including insulin-like growth factor-1, hepatocyte growth factor, interleukin 6 (IL6), and tumor necrosis factor α (TNF-α), were elevated. In addition, the proliferative signaling pathways, Ki-67-labeling index, proliferating cell nuclear antigen (PCNA)-labeling index, mitotic index, and liver/body weight ratio were increased under thrombocytosis. The platelet-induced regeneration was independent of TPO because increases in the Ki-67-labeling and PCNA-labeling indexes were eliminated after reducing platelet counts by antiplatelet serum in rats administered with TPO. For IRI, thrombocytosis did not aggravate oxidative stress or downstream signaling pathways, necrosis, or apoptosis in the graft. After Kupffer cell (KC) depletion, the platelet-induced attenuation of serum aminotransferases, increased serum levels of IL6 and TNF-α, and proliferation-related signaling pathways were eliminated. Moreover, platelet accumulation in the graft decreased substantially. In experiment 2, a 20% partial LT was performed, and thrombocytosis improved postoperative survival. In conclusion, our results suggested that thrombocytosis stimulated graft regeneration and prolonged survival without aggregating IRI after partial LT, and KCs vitally contributed to platelet-derived regeneration. Platelet therapies to increase perioperative platelet counts may improve the outcomes after LDLT.

Endothelium-dependent remote signaling in ischemia and reperfusion: Alterations in the cardiometabolic continuum

Intact endothelial function plays a fundamental role for the maintenance of cardiovascular (CV) health. The endothelium is also involved in remote signaling pathway-mediated protection against ischemia/reperfusion (I/R) injury. However, the transfer of these protective signals into clinical practice has been hampered by the complex metabolic alterations frequently observed in the cardiometabolic continuum, which affect redox balance and inflammatory pathways. Despite recent advances in determining the distinct roles of hyperglycemia, insulin resistance (InR), hyperinsulinemia, and ultimately diabetes mellitus (DM), which define the cardiometabolic continuum, our understanding of how these conditions modulate endothelial signaling remains challenging. It is widely accepted that endothelial cells (ECs) undergo functional changes within the cardiometabolic continuum. Beyond vascular tone and platelet-endothelium interaction, endothelial dysfunction may have profound negative effects on outcome during I/R. In this review, we summarize the current knowledge of the influence of hyperglycemia, InR, hyperinsulinemia, and DM on endothelial function and redox balance, their influence on remote protective signaling pathways, and their impact on potential therapeutic strategies to optimize protective heterocellular signaling.

MicroRNA-144 promotes remote limb ischemic preconditioning-mediated neuroprotection against ischemic stroke via PTEN/Akt pathway

Ischemic stroke is a refractory disease generally caused by cerebral ischemic injury. Remote ischemic preconditioning (RIPC) caused by transient ischemia and reperfusion of the femoral artery exerts a protective effect on ischemic stroke-induced brain injury. This study was designed to investigate the potential molecular mechanism of RIPC-mediated neuroprotection, namely, the biological effects of microRNA-144 on RIPC in mice with ischemic stroke and its effects on PTEN and Akt signaling pathways. Healthy adult C57BL6 mice were selected for the establishment of middle cerebral artery occlusion (MCAO). One hour before the start, remote ischemic preconditioning of limbs was performed in mice. Brain edema and infarct volume were measured. The expressions of microRNA-144, PTEN, and Akt were measured. The results showed that, compared with MCAO group, the RIPC group protected mice from cerebral ischemia-reperfusion injury, systemic accumulation of inflammatory cytokines, and accelerated apoptosis of parenchymal cells. In RIPC group, PTEN expression decreased, and mir-144 and Akt expression increased. The level of phosphorylated PTEN in the transfected microRNA-144 inhibitor group increased and the level of phosphorylated Akt reduced significantly. In conclusion, our results suggest that microRNA-144 may play a protective role in remote ischemic pretreatment by downregulating PTEN and upregulating Akt, suggesting that microRNA-144 via PTEN/Akt pathway may be of therapeutic significance in ischemic stroke.

Ischemic Preconditioning Improves Microvascular Endothelial Function in Remote Vasculature by Enhanced Prostacyclin Production

BACKGROUND The mechanisms underlying the effect of preconditioning on remote microvasculature remains undisclosed. The primary objective was to document the remote effect of ischemic preconditioning on microvascular function in humans. The secondary objective was to test if exercise also induces remote microvascular effects. METHODS AND RESULTS A total of 12 healthy young men and women participated in 2 experimental days in a random counterbalanced order. On one day the participants underwent 4×5 minutes of forearm ischemic preconditioning, and on the other day they completed 4×5 minutes of hand-grip exercise. On both days, catheters were placed in the brachial and femoral artery and vein for infusion of acetylcholine, sodium nitroprusside, and epoprostenol. Vascular conductance was calculated from blood flow measurements with ultrasound Doppler and arterial and venous blood pressures. Ischemic preconditioning enhanced (P<0.05) the remote vasodilator response to intra-arterial acetylcholine in the leg at 5 and 90 minutes after application. The enhanced response was associated with a 6-fold increase (P<0.05) in femoral venous plasma prostacyclin levels and with a transient increase (P<0.05) in arterial plasma levels of brain-derived neurotrophic factor and vascular endothelial growth factor. In contrast, hand-grip exercise did not influence remote microvascular function. CONCLUSIONS These findings demonstrate that ischemic preconditioning of the forearm improves remote microvascular endothelial function and suggest that one of the underlying mechanisms is a humoral-mediated potentiation of prostacyclin formation.

Remote Ischemic Preconditioning in a Cirrhotic Patient Undergoing Major Hepatectomy

Remote ischemic preconditioning (RIPC) has been shown to reduce ischemic reperfusion injury for patients undergoing hepatectomy for colorectal liver metastasis. We present a case of a 69-year-old male who underwent right hepatectomy for a multifocal hepatocellular carcinoma of the right liver and concomitant liver cirrhosis (Child-Pugh stage A). We performed portal vein embolization prior to surgery and intraoperative RIPC of the iliac vessels. The postoperative course after major hepatectomy went uneventful.

Remote ischemic preconditioning inhibits platelet αIIb β3 activation in coronary artery disease patients receiving dual antiplatelet therapy: A randomized trial

OBJECTIVES

We investigated whether remote ischemic preconditioning (RIPC) inhibits agonist-induced conformational activation of platelet αIIb β3 in patients with coronary artery disease already receiving conventional antiplatelet therapy.

PATIENTS/METHODS

Consecutive patients with angiographically confirmed coronary artery disease were randomized to RIPC or sham treatment. Venous blood was collected before and immediately after RIPC/sham. Platelet aggregometry (ADP, arachidonic acid) and whole blood platelet flow cytometry was performed for CD62P, CD63, active αIIb β3 (PAC-1 binding) before and after stimulation with ADP, thrombin ± collagen, or PAR-1 thrombin receptor agonist.

RESULTS

Patients (25 RIPC, 23 sham) were well matched, 83% male, age (mean ± standard deviation) 63.3 ± 13.2 years, 95% aspirin, 81% P2Y12 inhibitor. RIPC did not affect platelet aggregation, nor agonist-induced expression of CD62P, but selectively and significantly decreased αIIb β3 activation after stimulation with either PAR-1 agonist peptide or the combination of thrombin + collagen, but not after ADP nor thrombin alone. The effect of RIPC on platelet αIIb β3 activation was evident in patients receiving both aspirin and P2Y12 inhibitor, and was not associated with an increase in vasodilator-stimulated phosphoprotein phosphorylation.

CONCLUSIONS

Remote ischemic preconditioning inhibits conformational activation of platelet αIIb β3 in response to exposure to thrombin and collagen in patients with coronary artery disease receiving dual antiplatelet therapy. These findings indicate agonist-specific inhibition of platelet activation by RIPC in coronary artery disease that is not obviated by the prior use of P2Y12 inhibitors.

Vagus Nerve Stimulation Alleviates Hepatic Ischemia and Reperfusion Injury by Regulating Glutathione Production and Transformation

Inflammation and oxidative stress are pivotal mechanisms for the pathogenesis of ischemia and reperfusion injury (IRI). Vagus nerve stimulation (VNS) may participate in maintaining oxidative homeostasis and response to external stimulus or injury. We investigated whether the in vivo VNS can protect the liver from IRI. In this study, hepatic IRI were induced by ligating the vessels supplying the left and middle lobes of the liver, which underwent 1 h occlusion followed with 24 h reperfusion. VNS was initiated 15 min after ischemia and continued 30 min. Hepatic function, histology, and apoptosis rates were evaluated after 24 h reperfusion. Compared with the IRI group, VNS significantly improved hepatic function. The protective effect was accompanied by a reduction in histological damage in the ischemic area, and the apoptosis rate of hepatocytes has considerable reduction. To find the underlying mechanism, proteomic analysis was performed and differential expression of glutathione synthetase (GSS) and glutathione S-transferase (GST) was observed. Subsequently, test results indicated that VNS upregulated the expression of mRNA and protein of GSS and GST. Meanwhile, VNS increased the plasma levels of glutathione and glutathione peroxidases. We found that VNS alleviated hepatic IRI by upregulating the antioxidant glutathione via the GSS/glutathione/GST signaling pathway.

Remote Ischemic Preconditioning and Diazoxide Protect from Hepatic Ischemic Reperfusion Injury by Inhibiting HMGB1-Induced TLR4/MyD88/NF-κB Signaling

Remote ischemic preconditioning (RIPC) is known to have a protective effect against hepatic ischemia-reperfusion (IR) injury in animal models. However, the underlying mechanism of action is not clearly understood. This study examined the effectiveness of RIPC in a mouse model of hepatic IR and aimed to clarify the mechanism and relationship of the ATP-sensitive potassium channel (K_ATP) and HMGB1-induced TLR4/MyD88/NF-κB signaling. C57BL/6 male mice were separated into six groups: (i) sham-operated control, (ii) IR, (iii) RIPC+IR, (iv) RIPC+IR+glyburide (K_ATP blocker), (v) RIPC+IR+diazoxide (K_ATP opener), and (vi) RIPC+IR+diazoxide+glyburide groups. Histological changes, including hepatic ischemia injury, were assessed. The levels of circulating liver enzymes and inflammatory cytokines were measured. Levels of apoptotic proteins, proinflammatory factors (TLR4, HMGB1, MyD88, and NF-κB), and IκBα were measured by Western blot and mRNA levels of proinflammatory cytokine factors were determined by RT-PCR. RIPC significantly decreased hepatic ischemic injury, inflammatory cytokine levels, and liver enzymes compared to the corresponding values observed in the IR mouse model. The K_ATP opener diazoxide + RIPC significantly reduced hepatic IR injury demonstrating an additive effect on protection against hepatic IR injury. The protective effect appeared to be related to the opening of K_ATP, which inhibited HMGB1-induced TRL4/MyD88/NF-kB signaling.

Effect of Remote Ischemic Preconditioning on Patients Undergoing Elective Major Vascular Surgery: A Systematic Review and Meta-analysis

BACKGROUND

Whether remote ischemic preconditioning (RIPC), through several cycles of ischemia-reperfusion, can generate endogenous protective substances to protect patients undergoing elective major vascular surgery remains unclear. The results derived from many randomized controlled trials (RCTs) have been discrepant.

METHODS

PubMed (1966 to May 2018) and EMBASE (1966 to May 2018) databases were searched to identify all published RCTs that assessed the effect of RIPC in patients undergoing elective major vascular surgery. Then, we performed a systematic review and meta-analysis to merge the outcomes of RIPC procedures from each RCT, which included all-cause mortality, myocardial infarction (MI), acute kidney injury (AKI), and/or new-onset arrhythmia.

RESULTS

A total of 909 patients were enrolled from 10 eligible studies that were conducted from 2007 through 2016. A fixed effect model was utilized in this study to pool each effect size. Pooled analyses of all RCTs showed that RIPC did not reduce the incidence of all-cause mortality (pooled risk ratio [RR] 1.36, 95% confidence interval [CI] 0.63-2.92, P = 0.56), MI (pooled RR 0.77, 95% CI 0.48-1.22, P = 0.38), AKI (pooled RR 0.93, 95% CI 0.68-1.27, P = 0.10), or new-onset arrhythmia (pooled RR 1.47, 95% CI 0.83-2.60, P = 0.52) compared with the control treatment. The publication bias detected by Begg's test was low.

CONCLUSIONS

There is no prominent evidence to support the hypothesis that RIPC can provide perioperative protection to patients undergoing elective major vascular surgery. Therefore, the routine use of RIPC to reduce the incidence of perioperative complications of these operations may not be recommended.

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.

Exogenous melatonin protects small-for-size liver grafts by promoting monocyte infiltration and releases interleukin-6

Defective regeneration of small-for-size (SFS) liver remnants and partial grafts remains a key limiting factor in the application of liver surgery and transplantation. Exogenous melatonin (MLT) has protective effects on hepatic ischemia-reperfusion injury (IRI), but its influence on graft regeneration is unknown. The aim of the study is to investigate the role of MLT in IRI and graft regeneration in settings of partial liver transplantation. We established three mouse models to study hepatic IRI and regeneration associated with partial liver transplantation: (I) IR+PH group: 60 minutes liver ischemia (IR) plus 2/3 hepatectomy (PH); (II) IR+exPH group: 60 minutes liver IR plus extended hepatectomy (exPH) associated with the SFS syndrome; (III) SFS-LT group: Arterialized 30% SFS liver transplant. Each group was divided into MLT or vehicle-treated subgroups. Hepatic injury, inflammatory signatures, liver regeneration, and animal survival rates were assessed. MLT reduced liver injury, enhanced liver regeneration, and promoted interleukin (IL) 6, IL10, and tumor necrosis factor-α release by infiltrating, inflammatory Ly6C+ F4/80+ monocytes in the IR+PH group. MLT-induced IL6 significantly improved hepatic microcirculation and survival in the IR+exPH model. In the SFS-LT group, MLT promoted graft regeneration and increased recipient survival along with increased IL6/GP130-STAT3 signaling. In IL6^-/- mice, MLT failed to promote liver recovery, which could be restored through recombinant IL6. In the IR+exPH and SFS-LT groups, inhibition of the IL6 co-receptor GP130 through SC144 abolished the beneficial effects of MLT. MLT ameliorates SFS liver graft IRI and restores regeneration through monocyte-released IL6 and downstream IL6/GP130-STAT3 signaling.

Effects of the gut-liver axis on ischaemia-mediated hepatocellular carcinoma recurrence in the mouse liver

BACKGROUND & AIMS

There is growing evidence that liver graft ischemia-reperfusion (I/R) is a risk factor for hepatocellular carcinoma (HCC) recurrence, but the mechanisms involved are unclear. Herein, we tested the hypothesis that mesenteric congestion resulting from portal blood flow interruption induces endotoxin-mediated Toll-like receptor 4 (Tlr4) engagement, resulting in elevated liver cancer burden. We also assessed the role of remote ischemic preconditioning (RIPC) in this context.

METHODS

C57Bl/6j mice were exposed to standardized models of liver I/R injury and RIPC, induced by occluding the hepatic and femoral blood vessels. HCC was induced by injecting RIL-175 cells into the portal vein. We further evaluated the impact of the gut-liver axis (lipopolysaccharide (LPS)-Tlr4 pathway) in this context by studying mice with enhanced (lipopolysaccharide infusion) or defective (Tlr4^-/- mice, gut sterilization, and Tlr4 antagonist) Tlr4 responses.

RESULTS

Portal triad clamping provoked upstream mesenteric venous engorgement and increased bacterial translocation, resulting in aggravated tumor burden. RIPC prevented this mechanism by preserving intestinal integrity and reducing bacterial translocation, thereby mitigating HCC recurrence. These observations were linked to the LPS-Tlr4 pathway, as supported by the high and low tumor burden displayed by mice with enhanced or defective Tlr4 responses, respectively.

CONCLUSIONS

Modulation of the gut-liver axis and the LPS-Tlr4 response by RIPC, gut sterilization, and Tlr4 antagonism represents a potential therapeutic target to prevent I/R lesions, and to alleviate HCC recurrence after liver transplantation and resection.

LAY SUMMARY

Cancer recurrence can occur after liver resection or liver transplantation for hepatocellular carcinoma (HCC). This study suggests that intestinal venous congestion, which often occurs during liver surgery, favors the translocation of gut-derived bacterial products in the portal vein, thereby facilitating cancer recurrence by enhancing the signaling of Toll-like receptor 4 in the liver. Using a mouse model of HCC recurrence, we show that strategies that (i) reduce bacterial translocation (by gut decontamination, or by protecting the intestine from venous ischemia damage) or (ii) inhibit Tlr4 signaling in the liver, could reduce cancer recurrence.

Remote ischemic preconditioning fails to reduce infarct size in the Zucker fatty rat model of type-2 diabetes: role of defective humoral communication

Remote ischemic preconditioning (RIPC), the phenomenon whereby brief ischemic episodes in distant tissues or organs render the heart resistant to infarction, has been exhaustively demonstrated in preclinical models. Moreover, emerging evidence suggests that exosomes play a requisite role in conveying the cardioprotective signal from remote tissue to the myocardium. However, in cohorts displaying clinically common comorbidities-in particular, type-2 diabetes-the infarct-sparing effect of RIPC may be confounded for as-yet unknown reasons. To investigate this issue, we used an integrated in vivo and in vitro approach to establish whether: (1) the efficacy of RIPC is maintained in the Zucker fatty rat model of type-2 diabetes, (2) the humoral transfer of cardioprotective triggers initiated by RIPC are transported via exosomes, and (3) diabetes is associated with alterations in exosome-mediated communication. We report that a standard RIPC stimulus (four 5-min episodes of hindlimb ischemia) reduced infarct size in normoglycemic Zucker lean rats, but failed to confer protection in diabetic Zucker fatty animals. Moreover, we provide novel evidence, via transfer of serum and serum fractions obtained following RIPC and applied to HL-1 cardiomyocytes subjected to hypoxia-reoxygenation, that diabetes was accompanied by impaired humoral communication of cardioprotective signals. Specifically, our data revealed that serum and exosome-rich serum fractions collected from normoglycemic rats attenuated hypoxia-reoxygenation-induced HL-1 cell death, while, in contrast, exosome-rich samples from Zucker fatty rats did not evoke protection in the HL-1 cell model. Finally, and unexpectedly, we found that exosome-depleted serum from Zucker fatty rats was cytotoxic and exacerbated hypoxia-reoxygenation-induced cardiomyocyte death.

Ischaemic preconditioning - Current knowledge and potential future applications after 30 years of experience

Ischaemic preconditioning (IPC) phenomenon has been known for thirty years. During that time several studies showed that IPC provided by brief ischaemic and reperfusion episodes prior to longer ischaemia can bestow a protective effect to both preconditioned and also remote organs. IPC affecting remote organs is called remote ischaemic preconditioning. Initially, most IPC studies were focused on enhancing myocardial resistance to subsequent ischaemia and reperfusion injury. However, preconditioning was found to be a universal phenomenon and was observed in various organs and tissues including the heart, liver, brain, retina, kidney, skeletal muscles and intestine. Currently, there are a lot of simultaneous studies are underway aiming at finding out whether IPC can be helpful in protecting these organs. The mechanism of local and remote IPC is complex and not well known. Several triggers, intracellular pathways and effectors, humoral, neural and induced by genetic changes may be considered potential pathways in the protective activity of local and remote IPC. Local and remote IPC mechanism may potentially serve as heart protection during cardiac surgery and may limit the infarct size of the myocardium, can be a strategy for preventing the development of acute kidney injury development and liver damage during transplantation, may protect the brain against ischaemic injury. In addition, the method is safe, non-invasive, cheap and easily applicable. The main purpose of this review article is to present new advances which would help to understand the potential mechanism of IPC. It also discusses both its potential applications and utility in clinical settings.

Remote Ischemic Preconditioning: A Novel Strategy in Rescuing Older Livers From Ischemia-reperfusion Injury in a Rodent Model

OBJECTIVES

The aim of this study was to determine whether remote ischemic preconditioning (RIPC) protects aged liver against ischemia reperfusion (IR).

SUMMARY OF BACKGROUND DATA

The demands for liver surgery in an aging population are growing. Clamping of vessels to prevent blood loss is integral to liver surgery, but the resulting IR injury (IRI) augments postoperative complications. More so, sensitivity to hepatic IRI increases with age; however, no strategies have been developed that specifically protect old liver. RIPC, a novel protective approach, was performed distant to the surgical site. Whether RIPC may also protect old liver from IRI is unknown.

METHODS

RIPC to the femoral vascular bundle was compared against direct ischemic preconditioning (IPC) and the standard of care intermittent clamping (IC) using a model of partial hepatic ischemia in mice aged 20 to 24 months. Liver injury was measured 6 hours after reperfusion. Protective signaling (serotonin-Vegf-Il10/Mmp8 axis, Kupffer cell polarization) was assessed immediately after preconditioning. Neutralizing antibody was used to test the role of Vegf. Hepatic vasculature was examined by electron microscopy.

RESULTS

RIPC was superior over other strategies in protecting old liver from IRI, with standard IPC approaches being ineffective. RIPC induced the strongest elevations in circulating Vegf, and Vegf inhibition dampened protective signaling and abrogated the protective effects. RIPC was further associated with improvements in vascular functionality.

CONCLUSIONS

RIPC is highly effective in protecting old liver from ischemic insults, mainly owing to its ability to induce circulating Vegf. These findings warrant efforts toward clinical translation.

Remote ischemic conditioning protects against acetaminophen-induced acute liver injury in mice

AIM

Acetaminophen (APAP) overdose is a major cause of drug-induced acute liver failure. Studies have shown that remote ischemic pre- and post-conditioning (R-IPC and R-IPOST) can protect the liver against ischemia-reperfusion (I/R) and lipopolysaccharide-induced injuries. The aim of this study was to investigate the effect of R-IPC and R-IPOST on APAP-induced hepatotoxicity in mice.

METHODS

Mice were randomized (n = 6 per group) to seven major groups: (i) normal control; (ii) sham operated; (iii) APAP; (iv) R-IPC + APAP; (v) R-IPC + APAP + zinc protoporphyrin (ZnPP); (vi) R-IPOST + APAP; and (vii) R-IPOST + APAP + ZnPP. Sixteen hours after APAP treatment, mouse liver and serum were collected to determine the severity of liver injury.

RESULTS

The results showed that R-IPC and R-IPOST significantly decreased APAP-induced serum levels of alanine aminotransferase, aspartate aminotransferase, tumor necrosis factor-α, interleukin-6, and hepatic malondialdehyde, as well as nitrotyrosine formation. Both R-IPC and R-IPOST could improve the hepatic superoxide dismutase, glutathione, and glutathione peroxidase activities and depress the expressions of pro-inflammatory associated proteins, such as inducible nitric oxide synthetase and nuclear factor-κB. They could also increase heme oxygenase-1 expression; however, ZnPP could counteract this protective effect.

CONCLUSION

Remote ischemic conditioning has significant therapeutic potential in APAP-induced hepatotoxicity by inhibiting oxidative stress and inflammation and promoting heme oxygenase-1 expression.

Effect of remote ischemic preconditioning in the expression of IL-6 and IL-10 in a rat model of liver ischemia-reperfusion injury

PURPOSE

To study the effect of remote ischemic preconditioning (RIPC) in ischemia-reperfusion (I/R) liver injury and in the expression of IL-6 and IL-10 in a rat model.

METHODS

Thirty-six male rats were divided in three groups: Sham; I/R injury, a 45 minutes lobar liver ischemia and reperfusion; and RIPC, six cycles of four minutes of ischemia and four minutes of reperfusion on the right hindlimb followed by a 45 minutes lobar liver ischemia and reperfusion. Tissue and blood samples were collected after 1h and 3h of reperfusion for histopathological study, plasma cytokines and alanine aminotransferase (ALT) measurement.

RESULTS

The histopathological study demonstrated a significant reduction in liver necrosis in the RIPC group (p<0,001). The ALT levels were also significant lower in the RIPC group (p<0.01). The cytokines assessment showed that IL-6 levels were increased in the RIPC group after 1h of reperfusion, in comparison to the I/R group (p<0.05). Interleukin-10 levels in RIPC groups did not differ significantly from I/R group.

CONCLUSIONS

Remote ischemic preconditioning is effective in decreasing liver necrosis in a rat model of ischemia-reperfusion. The IL-6 expression is up-regulated and peaked at 60 min of reperfusion. There was no difference in IL-10 expression between the groups.

Cepharanthine alleviates liver injury in a rodent model of limb ischemia-reperfusion

OBJECTIVES

Limb ischemia-reperfusion (I/R) causes remote organ injury (e.g., liver injury). Oxidation and inflammation are crucial mechanisms. We investigated the effects of cepharanthine, a potent antioxidative and anti-inflammatory drug, on alleviating liver injury induced by limb I/R.

METHODS

Twenty-four adult male Sprague-Dawley rats were randomized to receive sham operation (Sham), Sham plus cepharanthine, I/R, or I/R plus cepharanthine and designated as the Sham, Sham+Cep, I/R, or I/R+Cep group, respectively (n = 6 in each group). I/R was induced by applying rubber band tourniquets high around each hind limb for 3 hours followed by reperfusion for 24 hours.

RESULTS

The plasma levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) of the Sham and Sham+Cep groups were low, and the levels of AST and ALT of the I/R group were significantly higher than those of the Sham group (both p<0.001). By contrast, the AST and ALT of the I/R+Cep group were significantly lower than those of the I/R group (both p<0.001). The hepatic levels of nitric oxide (NO), malondialdehyde (MDA), macrophage inflammatory protein 2 (MIP-2), interleukin-6 (IL-6), and cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) of the Sham and Sham+Cep groups were also low. As expected, the NO, MDA, MIP-2, IL-6, and COX-2/PGE2 of the I/R group were significantly higher than those of the Sham group (all p<0.001). By contrast, the NO, MDA, MIP-2, IL-6, and COX-2/PGE2 of the I/R+Cep group were significantly lower than those of the I/R group (all p<0.05).

CONCLUSION

Cepharanthine alleviates liver injury in a rodent model of limb I/R. The mechanisms may involve reducing oxidation and inflammation.

Mitochondrial Dysfunction and Autophagy in Hepatic Ischemia/Reperfusion Injury

Ischemia/reperfusion (I/R) injury remains a major complication of liver resection, transplantation, and hemorrhagic shock. Although the mechanisms that contribute to hepatic I/R are complex and diverse involving the interaction of cell injury in hepatocytes, immune cells, and endothelium, mitochondrial dysfunction is a cardinal event culminating in hepatic reperfusion injury. Mitochondrial autophagy, so-called mitophagy, is a key cellular process that regulates mitochondrial homeostasis and eliminates damaged mitochondria in a timely manner. Growing evidence accumulates that I/R injury is attributed to defective mitophagy. This review aims to summarize the current understanding of autophagy and its role in hepatic I/R injury and highlight the various therapeutic approaches that have been studied to ameliorate injury.

Platelet aggregation but not activation and degranulation during the acute post-ischemic reperfusion phase in livers with no underlying disease

BACKGROUND

Platelets and P-selectin (CD62P) play an unequivocal role in the pathology of hepatic ischemia/reperfusion (I/R) injury. Inhibition or knock-out of P-selectin or immunodepletion of platelets results in amelioration of post-ischemic inflammation, reduced hepatocellular damage, and improved survival. However, P-selectin expression on platelets and endothelial cells, which concurs with platelet activation, has never been clearly demonstrated in I/R-subjected livers.

AIMS

To determine whether platelets become activated and degranulate in the acute phase of liver I/R and whether the platelets interact with neutrophils.

METHODS

Hepatic I/R was induced in male C57BL/6J mice (N = 12) using 37.5-min ischemia time. Platelets, endothelial cells, and neutrophils were fluorescently labeled by systemic administration of non-blocking antibodies. Cell kinetics were monitored by intravital spinning disk confocal microscopy during 90 min of reperfusion. Image analysis and quantification was performed with dedicated software.

RESULTS

Platelets adhered to sinusoids more extensively in post-ischemic livers compared to livers not subjected to I/R and formed aggregates, which occurred directly after ischemia. Platelets and endothelial cells did not express P-selectin in post-ischemic livers. There was no interaction between platelets and neutrophils.

CONCLUSIONS

Platelets aggregate but do not become activated and do not degranulate in post-ischemic livers. There is no platelet-neutrophil interplay during the early reperfusion phase in a moderate model of hepatic I/R injury. The mechanisms underlying the biological effects of platelets and P-selectin in this setting warrant further investigation.

RELEVANCE FOR PATIENTS

I/R in surgical liver patients may compromise outcome due to post-ischemic oxidative stress and sterile inflammation. Both processes are mediated in part by platelets. Understanding platelet function during I/R is key to developing effective interventions for I/R injury and improving clinical outcomes.

Plasma from human volunteers subjected to remote ischemic preconditioning protects human endothelial cells from hypoxia-induced cell damage

Short repeated cycles of peripheral ischemia/reperfusion (I/R) can protect distant organs from subsequent prolonged I/R injury; a phenomenon known as remote ischemic preconditioning (RIPC). A RIPC-mediated release of humoral factors might play a key role in this protection and vascular endothelial cells are potential targets for these secreted factors. In the present study, RIPC-plasma obtained from healthy male volunteers was tested for its ability to protect human umbilical endothelial cells (HUVEC) from hypoxia–induced cell damage. 10 healthy male volunteers were subjected to a RIPC-protocol consisting of 4 × 5 min inflation/deflation of a blood pressure cuff located at the upper arm. Plasma was collected before (T0; control), directly after (T1) and 1 h after (T2) the RIPC procedure. HUVEC were subjected to 24 h hypoxia damage and simultaneously incubated with 5 % of the respective RIPC-plasma. Cell damage was evaluated by lactate dehydrogenase (LDH)-measurements. Western blot experiments of hypoxia inducible factor 1 alpha (HIF1alpha), phosphorylated signal transducer and activator of transcription 5 (STAT5), protein kinase B (AKT) and extracellular signal-related kinase 1/2 (ERK-1/2) were performed. Furthermore, the concentrations of hVEGF were evaluated in the RIPC-plasma by sandwich ELISA. Hypoxia–induced cell damage was significantly reduced by plasma T1 (p = 0.02 vs T0). The protective effect of plasma T1 was accompanied by an augmentation of the intracellular HIF1alpha (p = 0.01 vs T0) and increased phosphorylation of ERK-1/2 (p = 0.03 vs T0). Phosphorylation of AKT and STAT5 remained unchanged. Analysis of the protective RIPC-plasma T1 showed significantly reduced levels of hVEGF (p = 0.01 vs T0). RIPC plasma protects endothelial cells from hypoxia–induced cell damage and humoral mediators as well as intracellular HIF1alpha may be involved.