Concepts of hypoxic NO signaling in remote ischemic preconditioning

Remote ischaemic preconditioning - translating cardiovascular benefits to humans

Remote ischaemic preconditioning (RIPC), induced by intermittent periods of limb ischaemia and reperfusion, confers cardiac and vascular protection from subsequent ischaemia–reperfusion (IR) injury. Early animal studies reliably demonstrate that RIPC attenuated infarct size and preserved cardiac tissue. However, translating these adaptations to clinical practice in humans has been challenging. Large clinical studies have found inconsistent results with respect to RIPC eliciting IR injury protection or improving clinical outcomes. Follow‐up studies have implicated several factors that potentially affect the efficacy of RIPC in humans such as age, fitness, frequency, disease state and interactions with medications. Thus, realizing the clinical potential for RIPC may require a human experimental model where confounding factors are more effectively controlled and underlying mechanisms can be further elucidated. In this review, we highlight recent experimental findings in the peripheral circulation that have added valuable insight on the mechanisms and clinical benefit of RIPC in humans. Central to this discussion is the critical role of timing (i.e. immediate vs. delayed effects following a single bout of RIPC) and the frequency of RIPC. Limited evidence in humans has demonstrated that repeated bouts of RIPC over several days uniquely improves vascular function beyond that observed with a single bout alone. Since changes in resistance vessel and microvascular function often precede symptoms and diagnosis of cardiovascular disease, repeated bouts of RIPC may be promising as a preclinical intervention to prevent or delay cardiovascular disease progression.

Adaptation to oxidative stress at cellular and tissue level

Several in vitro and in vivo investigations have already proved that cells and tissues, when pre-exposed to low oxidative stress by different stimuli such as chemical, physical agents and environmental factors, display more resistance against subsequent stronger ischaemic injuries, resulting in an adaptive response known as ischaemic preconditioning (IPC). The aim of this review is to report the most recent knowledge about the complex adaptive mechanisms, including signalling transduction pathways, antioxidant systems, apoptotic and inflammation pathways, underlying cell protection against oxidative damage. In addition, an update about in vivo adaptation strategies in response to ischaemic/reperfusion episodes and brain trauma is also given.

Synergetic protective effect of remote ischemic preconditioning and prolyl 4‑hydroxylase inhibition in ischemic cardiac injury

It has been reported that hypoxia-inducible factor 1α (HIF-1α) serves a key role in the protective effect of remote ischemic preconditioning (RIP) in ischemia/reperfusion (I/R)-induced cardiac injury. Moreover, inhibition of prolyl 4-hydroxylase (PHD), an enzyme responsible for HIF-1α degradation, prevents I/R-induced cardiac injury. However, whether their protective effects are synergetic remains to be elucidated. The present study aimed to investigate the protective effect of RIP, PHD inhibition using dimethyloxalylglycine (DMOG) and their combination on I/R-induced cardiac injury. Rabbits were randomly divided into seven groups: i) Sham; ii) I/R; iii) lung RIP + I/R; iv) thigh RIP + I/R; v) DMOG + I/R; vi) DMOG + lung RIP + I/R; and vii) DMOG + thigh RIP + I/R. I/R models were established via 30 min left coronary artery occlusion and 3 h reperfusion. For lung/thigh RIP, rabbits received left pulmonary artery (or left limb) ischemia for 25 min and followed by release for 5 min. Some rabbits were administered 20 mg/kg DMOG. The results demonstrated that both lung/thigh RIP and DMOG significantly decreased myocardial infarct size, creatine kinase activity and myocardial apoptosis in I/R rabbits. Furthermore, the combination of RIP and PHD inhibition exerted synergetic protective effects on these aforementioned changes. The mechanistic study indicated that both treatments increased mRNA and protein expression levels of HIF-1α and its downstream regulators, including vascular endothelial growth factor (VEGF), AKT and endothelial nitric oxide synthase (eNOS). In conclusion, the present study demonstrated that RIP and PHD inhibition exerted synergetic protective effects on cardiac injury via activation of HIF-1α and the downstream VEGF/AKT-eNOS signaling pathway.

The Role of RIPC in Preventing Organ Damage, Inflammation, and Oxidative Stress during Lower Limb DSA: A Randomised Controlled Trial

Objective

Diagnostic digital subtraction angiography (DSA) and DSA with percutaneous transluminal angioplasty (DSA-PTA) are common procedures for diagnosing and treating symptomatic lower extremity arterial disease (LEAD). However, organ damage following DSA and DSA-PTA is often underrecognised and hence undiagnosed. To reduce the risk induced by invasive procedures in symptomatic LEAD patients, the method of remote ischemic preconditioning (RIPC) has been suggested. The aim of the current study was to assess the effect of RIPC intervention on the organ damage markers profile, oxidative stress, and inflammation biomarkers in LEAD patients undergoing DSA and DSA-PTA procedure.

Methods

The RIPC intervention was performed by inflating a standard blood pressure cuff on the patient's upper arm to 200 mmHg for 5 minutes four times with 5-minute perfusion between each cycle. The sham intervention was performed similarly, but the cuff was inflated to 20 mmHg. Changes in the cardiac and renal damage biomarkers' profile, oxidative stress, and inflammation biomarkers were recorded before and 24 hours after DSA or DSA-PTA.

Results

A total of 111 (RIPC 54, sham 57) patients with symptomatic LEAD scheduled for endovascular procedure were randomised, and 102 patients (RIPC 47, sham 55) completed the study protocol. RIPC significantly limited the increase of adiponectine levels after DSA and DSA-PTA, compared to sham intervention (p = 0.020), but CK-MB levels were markedly lower in the sham group (p = 0.047) after procedure. There was no significant difference between the RIPC and the sham group in mean changes in hs-troponin-T (p = 0.25), NT-proBNP (p = 0.24), creatinine (p = 0.76), eGFR (p = 0.61), urea (p = 0.95), beta-2-microglobuline (p = 0.34), or cystatine C (p = 0.24) levels.

Conclusion

In this controlled clinical study, RIPC failed to improve the profile of renal and cardiac biomarkers in patients with LEAD periprocedurally. RIPC significantly limits the rise in adiponectin levels and may influence the decrease of CK-MB levels 24 hours after endovascular procedure.

Cardioprotection by Humoral Factors Released After Remote Ischemic Preconditioning Depends on Anesthetic Regimen

OBJECTIVES

Remote ischemic preconditioning (RIPC) is a practicable and noninvasive method to protect the heart against ischemia reperfusion injury. Unfortunately results from clinical studies are not convincing. Propofol is suggested to be an inhibiting factor of cardioprotection by RIPC, but the underlying mechanism is still unknown. We investigated whether after RIPC the release of humoral factors and/or the direct cardioprotective effect at the myocardium is inhibited by propofol.

DESIGN

Randomized, prospective, blinded laboratory investigation.

SETTING

Experimental laboratory.

PATIENTS/SUBJECTS

Male Wistar rats.

INTERVENTIONS

Repetitive hind limb ischemia in rats-blood plasma transfers to isolated rat heart.

MEASUREMENTS AND MAIN RESULTS

In male Wistar rats (six groups, each n = 6/group), RIPC was induced by four cycles of 5 minutes bilateral hind limb ischemia alternately with 5 minutes of reperfusion. Blood samples were taken with (RIPC) and without RIPC (Con). Rats received continuous anesthesia with pentobarbital (Pento, 40 mg/kg body weight/hr) or propofol (Prop, 12 mg/kg body weight/hr), respectively. Cardioprotective properties of the blood plasma was investigated in the rat heart in vitro (six groups, each n = 6/group) perfused with Krebs-Henseleit buffer alone or with propofol (10 µM). Plasma was administered over 10 minutes before myocardial ischemia. All hearts underwent 33 minutes of global ischemia followed by 1 hour of reperfusion. At the end of the experiments, infarct size was determined by triphenyl-tetrazolium-chloride staining. RIPC plasma from pentobarbital anesthetized rats (Pento-RIPC) reduced infarct size from 64% (62-71%) (Pento-Con) to 34% (30-39%) (p < 0.0001). Infarct size with control plasma from propofol anesthetized rats was 59% (58-64%) (Prop-Con). RIPC plasma could not induce cardioprotection (Prop-RIPC: 63% [56-70%] ns vs Prop-Con). In contrast, RIPC plasma from pentobarbital anesthetized rats induced a significant infarct size reduction under propofol perfusion (Pento-RIPC: 34% [30-42%] vs Pento-Con: 54% [53-63%]; p < 0.0001).

CONCLUSIONS

Loss of cardioprotection by RIPC during propofol anesthesia depends on inhibition of release of humoral factors.

Inducible and endothelial nitric oxide synthase distribution and expression with hind limb per-conditioning of the rat kidney

INTRODUCTION

We recently reported that a series of brief hind limb ischemia and reperfusion (IR) at the beginning of renal ischemia (remote per-conditioning - RPEC) significantly attenuated the ischemia/reperfusion-induced acute kidney injury. In the present study, we investigated whether the nitric oxide synthase (NOS) pathway is involved in the RPEC protection of the rat ischemic kidneys.

MATERIAL AND METHODS

Male rats were subjected to right nephrectomy and randomized as: (1) sham, no additional intervention; (2) IR, 45 min of renal ischemia followed by 24 h reperfusion; (3) RPEC, four 5 min cycles of lower limb IR administered at the beginning of renal ischemia; (4) RPEC+L-NAME (a non-specific NOS inhibitor, 10 mg/kg, i.p.) (5) RPEC + 1400W (a specific iNOS inhibitor, 1 mg/kg, i.p.). After 24 h, blood, urine and tissue samples were collected.

RESULTS

The protective effect of RPEC on renal function, oxidative stress indices, pro-inflammatory marker expression and histopathological changes of kidneys subjected to 45 min ischemia were completely inhibited by pretreatment with L-NAME or 1400W. It was accompanied by increased iNOS and eNOS expression in the RPEC group compared with the IR group.

CONCLUSIONS

These findings suggest that the protective effects of RPEC on renal IR injury are closely dependent on the nitric oxide production after the reperfusion and both eNOS and iNOS are involved in this protection.

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.

Hypoxic conditioning in blood vessels and smooth muscle tissues: effects on function, mechanisms, and unknowns

Hypoxic preconditioning, the protective effect of brief, intermittent hypoxic or ischemic episodes on subsequent more severe hypoxic episodes, has been known for 30 yr from studies on cardiac muscle. The concept of hypoxic preconditioning has expanded; excitingly, organs beyond the heart, including the brain, liver, and kidney, also benefit. Preconditioning of vascular and visceral smooth muscles has received less attention despite their obvious importance to health. In addition, there has been no attempt to synthesize the literature in this field. Therefore, in addition to overviewing the current understanding of hypoxic conditioning, in the present review, we consider the role of blood vessels in conditioning and explore evidence for conditioning in other smooth muscles. Where possible, we have distinguished effects on myocytes from other cell types in the visceral organs. We found evidence of a pivotal role for blood vessels in conditioning and for conditioning in other smooth muscle, including the bladder, vascular myocytes, and gastrointestinal tract, and a novel response in the uterus of a hypoxic-induced force increase, which helps maintain contractions during labor. To date, however, there are insufficient data to provide a comprehensive or unifying mechanism for smooth muscles or visceral organs and the effects of conditioning on their function. This also means that no firm conclusions can be drawn as to how differences between smooth muscles in metabolic and contractile activity may contribute to conditioning. Therefore, we have suggested what may be general mechanisms of conditioning occurring in all smooth muscles and tabulated tissue-specific mechanistic findings and suggested ideas for further progress.

Remote Ischemic Preconditioning Decreases Oxidative Lung Damage After Pulmonary Lobectomy: A Single-Center Randomized, Double-Blind, Controlled Trial

BACKGROUND

During lobectomy in patients with lung cancer, the operated lung is often collapsed and hypoperfused. Ischemia/reperfusion injury may then occur when the lung is re-expanded. We hypothesized that remote ischemic preconditioning (RIPC) would decrease oxidative lung damage and improve gas exchange in the postoperative period.

METHODS

We conducted a single-center, randomized, double-blind trial in patients with nonsmall cell lung cancer undergoing elective lung lobectomy. Fifty-three patients were randomized to receive limb RIPC immediately after anesthesia induction (3 cycles: 5 minutes ischemia/5 minutes reperfusion induced by an ischemia cuff applied on the thigh) and/or control therapy without RIPC. Oxidative stress markers were measured in exhaled breath condensate (EBC) and arterial blood immediately after anesthesia induction and before RIPC and surgery (T0, baseline); during operated lung collapse, immediately before resuming two-lung ventilation (TLV) (T1); immediately after resuming TLV (T2); and 120 minutes after resuming TLV (T3). The primary outcome was 8-isoprostane levels in EBC at T1, T2, and T3. Secondary outcomes included the following: NO2+NO3, H2O2 levels, and pH in EBC and in blood (8-isoprostane, NO2+NO3) and pulmonary gas exchange variables (PaO2/FiO2, A-aDO2, a/A ratio, and respiratory index).

RESULTS

Patients subjected to RIPC had lower EBC 8-isoprostane levels when compared with controls at T1, T2, and T3 (differences between means and 95% confidence intervals): -15.3 (5.8-24.8), P = .002; -20.0 (5.5-34.5), P = .008; and -10.4 (2.5-18.3), P = .011, respectively. In the RIPC group, EBC NO2+NO3 and H2O2 levels were also lower than in controls at T2 and T1-T3, respectively (all P < .05). Blood levels of 8-isoprostane and NO2+NO3 were lower in the RIPC group at T2 (P < .05). The RIPC group had better PaO2/FiO2 compared with controls at 2 hours, 8 hours, and 24 hours after lobectomy in 95% confidence intervals for differences between means: 78 (10-146), 66 (14-118), and 58 (12-104), respectively.

CONCLUSIONS

Limb RIPC decreased EBC 8-isoprostane levels and other oxidative lung injury markers during lung lobectomy. RIPC also improved postoperative gas exchange as measured by PaO2/FiO2 ratio.

Dual character of flavonoids in attenuating and aggravating ischemia-reperfusion-induced myocardial injury

The concept that flavonoids exert cardioprotection against myocardial ischemia-reperfusion (I/R) injury has been acknowledged by a large body of evidence. However, recent studies reported cardiotoxic effects of certain flavonoids, while the underlying mechanisms have remained largely elusive. Flavonoids have been demonstrated to activate aryl hydrocarbon receptor (Ahr), which is implicated in an array of cell signaling processes. The present study examined the cardioprotective roles of quercetin (Qu) and β-naphthoflavone (β-NF) against I/R injury and explored whether the underlying mechanism proceeds via molecular signaling downstream of Ahr. An oxygen glucose deprivation/reoxygenation (OGD/R) model of I/R was established in myocardial H9c2 cells in the absence or presence of Qu or β-NF. Qu as well as β-NF reversed OGD/R-induced overproduction of reactive oxygen species by increasing the anti-oxidative capacity of the cells and protected them from lethal injury, as demonstrated by a decreased cell death rate, lactate hydrogenase leakage and caspase-3 activity as determined by flow cytometry, colorimetric assay and western blot analysis, respectively. Immunocytochemistry, co-immunoprecipitation and western blot assays collectively revealed that Qu and β-NF engendered the translocation of Ahr from the cytoplasm into the cell nucleus, where binding of Ahr with the Ahr nuclear translocator (ARNT) blocked its binding to hypoxia-inducible factor (HIF)-1α, which inhibited the cardioprotection of HIF-1α, including the induction of nitric oxide (NO) and inhibition of vascular endothelial growth factor (VEGF) production. Ahr knockdown recovered the binding of ARNT to HIF-1α and the generation of NO and VEGF. The results of the present study suggested a dual character of Qu and β-NF in the process of myocardial I/R.

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.

Mathematical relationships and their consequences between rat pulse waveform parameters and blood pressure during decreasing NO bioavailability

NEW FINDINGS

What is the central question of this study? We wanted to find out whether the relationship between rat arterial pulse waveform (APW) parameters and blood pressure could be described by known mathematical functions and find mathematical parameters for conditions of hypertension resulting from decreased NO bioavailability. What is the main finding and its importance? We found mathematical functions and their parameters that approximate the relationships of 12 APW parameters to systolic and diastolic blood pressure in conditions of decreased NO bioavailability. The results may assign APW parameters to decreased NO bioavailability, which may have predictive or diagnostic value. Information obtained from the arterial pulse waveform (APW) is useful for characterization of the cardiovascular system in particular (patho)physiological conditions. Our goal was to find out whether the relationships between rat APW parameters could be described by simple mathematical functions and to find mathematical parameters for conditions of hypertension resulting from decreased NO bioavailability. Therefore, we explored details of 14 left carotid APW parameters of anaesthetized male Wistar rats and mathematically characterized their relationship to systolic and diastolic blood pressure (BP) in conditions of a gradual reduction in NO bioavailability after administration of l-NAME. The right jugular vein of anaesthetized Wistar rats was cannulated for l-NAME administration. The left carotid artery was cannulated to detect the APW at high resolution. Here, we show the time-dependent parallel changes of 14 APW parameters before and after i.v. administration of l-NAME and present mathematical functions that approximate the relationships of 12 APW parameters to systolic and diastolic BP. Some APW parameters had minor (e.g. heart rate) or biphasic dependence on BP (e.g. relative level of the maximum rate of ventricular pressure decrease (dP/dt_min )), but all relationships, within a particular range of BP, could be approximated by known regression functions, as a linear function (e.g. pulse BP), exponential decay (e.g. relative level of the maximum rate of ventricular pressure increase (dP/dt_max )), exponential growth (systolic area), exponential rise to a maximum (relative augmentation index) or sigmoid function (e.g. increase of relative level of dP/dt_min ). The mathematical functions may assign APW parameters to decreased NO bioavailability. This may have predictive or diagnostic value.

MicroRNA-29a/b/c targets iNOS and is involved in protective remote ischemic preconditioning in an ischemia-reperfusion rat model of non-alcoholic fatty liver disease

Remote ischemic preconditioning (RIPC) protects against the injury that is incurred by ischemia and reperfusion (IR); however, the role of RIPC in liver IR injury in non-alcoholic fatty liver disease (NAFLD) remains unclear. In this study, a NAFLD rat model was utilized in a series of different surgical procedures and molecular experiments. Rats of the IR group and the RIPC+IR group exhibited more severe injury than NAFLD control rats (in which the liver was prodded following a median-incision laparotomy). The liver condition, measured by serum alanine transaminase and aspartate transaminase levels, of the RIPC+IR group was better than that of the IR group. In addition, alanine transaminase and aspartate transaminase levels were lower in the RIPC+IR group compared with the IR group (P<0.001). Flow cytometry revealed that the cell apoptosis ratio was significantly lower in the RIPC+IR group than in the IR group (P<0.001). Reverse transcription-polymerase chain reaction (RT-qPCR) was used to assess miR-29a/b/c levels, revealing that they were significantly reduced in the RIPC and RIPC+IR groups, but did not vary in the IR group compared with the control group. RT-qPCR also revealed that iNOS mRNA levels were not significantly different among any of the NAFLD groups; however, western blot analysis indicated that iNOS protein levels were increased in the RIPC group and the RIPC+IR group compared with the control and IR groups. A luciferase reporter assay demonstrated that transfection with miR-29a/b/c mimics significantly decreased the luciferase activities of plasmids containing the wild-type iNOS 3'-untranslated region (UTR) (relative fluorescence intensity: 0.47±0.06 for miR-29a, 0.36±0.07 for miR-29b, 0.41±0.04 for miR-29c; P<0.001), whereas the activities of plasmids containing the mutant iNOS 3'-UTR sequence were not markedly affected [relative fluorescence intensity: 0.99±0.08 for miR-29a (P=0.1349), 0.99±0.09 for miR-29b (P=0.1607), 0.97±0.07 for miR-29c (P=0.1824)]. This suggested that miR-29a/b/c downregulates iNOS by directly targeting its 3'-UTR. In summary, the results suggest that RIPC has a protective effect in NAFLD liver IR injury, which may be due to reduced miR-29a/b/c levels in the skeletal muscle, leading to increased iNOS and, therefore, nitric oxide.

Impact of Different Embolic Agents for Transarterial Chemoembolization (TACE) Procedures on Systemic Vascular Endothelial Growth Factor (VEGF) Levels

Background and Aims: Intermediate stage hepatocellular carcinoma (HCC) can be treated by transarterial chemoembolization (TACE). However, there appear to be side effects, such as induction of proangiogenic factors, e.g. vascular endothelial growth factor (VEGF), which have been shown to be associated with a poor prognosis. This prospective study was designed to compare serum VEGF level response after TACE with different embolic agents in patients with HCC. Methods: Patients were assigned to one of three different TACE regimens: degradable starch microspheres (DSM) TACE, drug-eluting bead (DEBDOX) TACE or Lipiodol TACE (cTACE). All patients received 50 mg doxorubicin/m² body surface area (BSA) during TACE. Serum VEGF levels were assessed before TACE treatment, 24 h post-treatment and 4 weeks later. Results: Twenty-two patients with 30 TACE treatments were enrolled. Compared to baseline VEGF levels, a marked increase was observed for 24 h post-TACE (164% of baseline level) and during the 4-week follow-up (170% of baseline level) only for the cTACE arm (p < 0.05). In contrast, the increase of serum VEGF levels were only 114% and 123% for DEBDOX and 121% and 124% for DSM, respectively. Conclusions: Conventional TACE using Lipiodol shows marked increase in blood levels of the proangiogenic factor VEGF, while DEBDOX and DSM TACE induce only a moderate VEGF response.