Preconditioning at a distance: Involvement of endothelial vasoactive substances in cardioprotection against ischemia-reperfusion injury

Up-regulation of miR-126 via DNA methylation in hypoxia-preconditioned endothelial cells may contribute to hypoxic tolerance of neuronal cells

BACKGROUND

Endothelial cells (ECs) can confer neuroprotection by secreting molecules. This study aimed to investigate whether DNA methylation contributes to the neuroprotective gene expression induced by hypoxia preconditioning (HPC) in ECs and to clarify that the secretion of molecules from HPC ECs may be one of the molecular mechanisms of neuroprotection.

METHODS

Human microvascular endothelial cell-1 (HMEC-1) was cultured under normal conditions (C), hypoxia(H), and hypoxia preconditioning (HPC), followed by the isolation of culture medium (CM). SY5Y cell incubated with the isolated CM from HMEC-1 was exposed to oxygen-glucose deprivation (OGD). The DNA methyltransferases (DNMTs), global methylation level, miR-126 and its promotor DNA methylation level in HMEC-1 were measured. The cell viability and cell injury in SY5Y were detected.

RESULTS

HPC decreased DNMTs level and global methylation level as well as increased miR-126 expression in HMEC-1. CM from HPC treated HMEC-1 also relieved SY5Y cell damage, while CM from HMEC-1 which over-expression of miR-126 can reduce injury in SY5Y under OGD condition.

CONCLUSIONS

These findings indicate EC may secrete molecules, such as miR-126, to execute neuroprotection induced by HPC through regulating the expression of DNMTs.

Baseline systolic blood pressure, hypertension history, and efficacy of remote ischemic conditioning

OBJECTIVE

We performed a post hoc exploratory analysis of Remote Ischemic Conditioning for Acute Moderate Ischemic Stroke (RICAMIS) to determine whether hypertension history and baseline systolic blood pressure (SBP) affect the efficacy of remote ischemic conditioning (RIC).

METHODS

Based on the full analysis set of RICAMIS, patients were divided into hypertension versus non-hypertension group, or <140 mmHg versus ≥140 mmHg group. Each group was further subdivided into RIC and control subgroups. The primary outcome was modified Rankin Scale (mRS) 0-1 at 90 days. Efficacy of RIC was compared among patients with hypertension versus nonhypertension history and SBP of <140 mmHg versus ≥140 mmHg. Furthermore, the interaction effect of treatment with hypertension and SBP was assessed.

RESULTS

Compared with control group, RIC produced a significantly higher proportion of patients with excellent functional outcome in the nonhypertension group (RIC vs. control: 65.7% vs. 57.0%, OR 1.45, 95% CI 1.06-1.98; p = 0.02), but no significant difference was observed in the hypertension group (RIC vs. control: 69.1% vs. 65.2%, p = 0.17). Similar results were observed in SBP ≥140 mmHg group (RIC vs. control: 68.0% vs. 61.2%, p = 0.009) and SBP <140 mmHg group (RIC vs. control: 65.6% vs. 64.7%, p = 0.77). No interaction effect of RIC on primary outcome was identified.

INTERPRETATION

Hypertension and baseline SBP did not affect the neuroprotective effect of RIC, but they were associated with higher probability of excellent functional outcome in patients with acute moderate ischemic stroke who received RIC treatment.

Protective effects of limb remote ischemic per-conditioning on the heart injury induced by renal ischemic-reperfusion through the interaction of the apelin with the RAS/iNOS pathway

Introduction

Remote ischemic conditioning upregulates endogenous protective pathways in response to ischemia-reperfusion injury. This study tested the hypothesis that limb remote ischemic per- conditioning (RIPerC) exerts cardioprotective effects via the renin-angiotensin system (RAS)/inducible nitric oxide synthase (iNOS)/apelin pathway.

Methods

Renal ischemia-reperfusion injury (I/R) was induced by bilateral occlusion of the renal pedicles for 60 minutes, followed by 24 hours of reperfusion; sham-operated rats served as controls. RIPerC was induced by four cycles (5 minutes) of limb ischemia-reperfusion along with bilateral renal ischemia. The functional disturbance was evaluated by renal (BUN and creatinine) and cardiac (troponin I and lactate dehydrogenase) injury biomarkers.

Results

Renal I/R injury increased renal and cardiac injury biomarkers that were reduced in the RIPerC group. Histopathological findings of the kidney and heart were also suggestive of amelioration injury-induced changes in the RIPerC group. Assessment of cardiac electrophysiology revealed that RIPerC ameliorated the decline in P wave duration without significantly affecting other cardiac electrophysiological changes. Further, renal I/R injury increased the plasma (322.40±34.01 IU/L), renal (8.27±1.10 mIU/mg of Protein), and cardiac (68.28±10.28 mIU/mg of protein) angiotensin-converting enzyme (ACE) activities in association with elevations in the plasma and urine nitrite (25.47±2.01 & 16.62±3.05 μmol/L) and nitrate (15.47±1.33 & 5.01±0.96 μmol/L) levels; these changes were reversed by RIPerC. Further, renal ischemia-reperfusion injury significantly (P=0.047) decreased the renal (but not cardiac) apelin mRNA expression, while renal and cardiac ACE2 (P<0.05) and iNOS (P=0.043) mRNA expressions were significantly increased compared to the sham group; these effects were largely reversed by RIPerC.

Conclusion

Our results indicated that RIPerC protects the heart against renal ischemia- reperfusion injury, likely via interaction of the apelin with the RAS/iNOS pathway.

Adeno-associated virus-mediated in vivo suppression of expression of EPHX2 gene modulates the activity of paraventricular nucleus neurons in spontaneously hypertensive rats

BACKGROUND

Hypertension can be attributed to increased sympathetic activities. Presympathetic neurons in the paraventricular nucleus (PVN) of the hypothalamus are capable of modulating sympathetic outflow, thus contributing to the pathogenesis of neurogenic hypertension. Epoxyeicosatrienoic acids (EETs) were reported to have anti-hypertensive effects, which could be degraded by soluble epoxide hydrolase (sEH), encoded by EPHX2. However, the potential effect of EETs on PVN neuron activity and the underlying molecular mechanism are largely unknown.

METHODS

Knockdown of EPHX2 in spontaneously hypertensive rats (SHRs) was achieved by tail-intravenous injection of AAV plasmid containing shRNA targeting EPHX2. Whole-cell patch clamp was used to record action potentials of PVN neurons. An LC-MS/MS System was employed to determine 14,15-EET levels in rat cerebrospinal fluid. qPCR and western blotting were applied to examine the expression level of EPHX2 in various tissues. ELISA and immunofluorescence staining were applied to examine the levels of ATP, D-serine and glial fibrillary acidic protein (GFAP) in isolated astrocytes.

RESULTS

The expression level of EPHX2 was higher, while the level of 14,15-EET was lower in SHRs than normotensive Wistar-Kyoto rats (WKY) rats. The spike firing frequency of PNV neurons in SHRs was higher than in WKY rats at a given stimulus current, which could be reduced by either EPHX2 downregulation or 14,15-EET administration. In isolated hypothalamic astrocytes, the elevated intracellular ATP or D-serine induced by Angiotensin II (Ang II) treatment could be rescued by 14,15-EET addition or 14,15-EET combing serine racemase (SR) downregulation by siRNA, respectively. Furthermore, 14,15-EET treatment reduced the Ang II-induced elevation of GFAP immunofluorescence.

CONCLUSIONS

The elevation of EET levels by EPHX2 downregulation reduced presympathetic neuronal activity in the PVN of SHRs, leading to a reduced sympathetic outflow in hypertension rats. The ATP/SR/D-serine pathway of astrocytes is involved in EET-mediated neuroprotection.

Chronic Limb Remote Ischemic Conditioning may have an Antihypertensive Effect in Patients with Hypertension

Hypertension is the leading preventable risk factor for all-cause morbidity and mortality worldwide. Despite antihypertensive medications have been available for decades, a big challenge we are facing is to increase the blood pressure (BP) control rate among the population. Therefore, it is necessary to search for new antihypertensive means to reduce the burden of disease caused by hypertension. Limb remote ischemic conditioning (LRIC) can trigger endogenous protective effects through transient and repeated ischemia on the limb to protect specific organs and tissues including the brain, heart, and kidney. The mechanisms of LRIC involve the regulation of the autonomic nervous system, releasing humoral factors, improvement of vascular endothelial function, and modulation of immune/inflammatory responses. These underlying mechanisms of LRIC may restrain the pathogenesis of hypertension through multiple pathways theoretically, leading to a potential decline in BP. Several existing studies have explored the impact of LRIC on BP, however, controversial findings were reported. To explore the potential antihypertensive effect of LRIC and the underlying mechanisms, we systematically reviewed the relevant articles to provide an insight into the novel therapy of hypertension.

Effects of Remote Ischaemic Preconditioning on the Internal Thoracic Artery Nitric Oxide Synthase Isoforms in Patients Undergoing Coronary Artery Bypass Grafting

Remote ischaemic preconditioning (RIPC) is a medical procedure that consists of repeated brief periods of transient ischaemia and reperfusion of distant organs (limbs) with the ability to provide internal organ protection from ischaemia. Even though RIPC has been successfully applied in patients with myocardial infarction during coronary revascularization (surgery/percutaneous angioplasty), the underlying molecular mechanisms are yet to be clarified. Thus, our study aimed to determine the role of nitric oxide synthase (NOS) isoforms in RIPC-induced protection (3 × 5 min of forearm ischaemia with 5 min of reperfusion) of arterial graft in patients undergoing urgent coronary artery bypass grafting (CABG). We examined RIPC effects on specific expression and immunolocalization of three NOS isoforms — endothelial (eNOS), inducible (iNOS) and neuronal (nNOS) in patients’ internal thoracic artery (ITA) used as a graft. We found that the application of RIPC protocol leads to an increased protein expression of eNOS, which was further confirmed with strong eNOS immunopositivity, especially in the endothelium and smooth muscle cells of ITA. The same analysis of two other NOS isoforms, iNOS and nNOS, showed no significant differences between patients undergoing CABG with or without RIPC. Our results demonstrate RIPC-induced upregulation of eNOS in human ITA, pointing to its significance in achieving protective phenotype on a systemic level with important implications for graft patency.

Non-Invasive Remote Ischemic Preconditioning May Protect the Gastric Mucosa Against Ischemia-Reperfusion-Induced Injury Through Involvement of Glucocorticoids

Remote ischemic preconditioning (RIPC) is one of the most effective approaches to attenuate tissue injury caused by severe ischemia-reperfusion (I/R). Experimental studies have demonstrated that RIPC is capable of producing a protective effect not only on heart, but also on brain, lungs, kidneys, liver, intestine, and stomach. We previously demonstrated that glucocorticoids participate in protective effect of local gastric ischemic preconditioning against I/R-induced gastric injury. In the present study we investigated whether RIPC may protect the gastric mucosa against I/R-induced injury through involvement of glucocorticoids. Anesthetized fasted Sprague Dawley male rats were exposed to prolonged gastric I/R (30 min occlusion of celiac artery followed by 3 h of reperfusion) alone or with preliminary brief RIPC (10 min non-invasive occlusion of right hind limb blood flow followed by reperfusion for 30 min). First, we investigated the effect of RIPC on I/R-induced injury by itself. Then to study the role of glucocorticoids similar experiments were carried out: 1) in rats pretreated with the inhibitor of glucocorticoid synthesis, metyrapone (30 mg/kg, i.p), and in control animals; 2) in adrenalectomized rats without or with corticosterone replacement (4 mg/kg, s.c.) and in sham-operated animals; 3) in rats pretreated with glucocorticoid receptor antagonist RU-38486 (20 mg/kg, s.c.) and in control animals. I/R induced corticosterone rise and resulted in the gastric erosion formation. RIPC significantly reduced the erosion area in control animals. Metyrapone injected shortly before RIPC caused a decrease in plasma corticosterone levels and prevented the gastroprotective effect of RIPC and, moreover, further aggravated the deleterious effect of I/R. Adrenalectomy performed 1 week before experiment created long-lasting corticosterone deficiency and had no effect on the gastroprotective effect of RIPC. Nevertheless, corticosterone replacement which mimics the corticosterone rise, similar to RIPS, significantly reduced erosion areas of gastric mucosa in adrenalectomized rats supporting the role of glucocorticoids in gastroprotection. RU-38486, which occupied glucocorticoid receptors, similar to metyrapone prevented the gastroprotective effect of RIPC and, moreover, further aggravated the deleterious effect of I/R. The results of the present study demonstrate for the first time that RIPC may protect the gastric mucosa against I/R-induced injury through involvement of glucocorticoids.

Cardioprotective effect of anisodamine against ischemia/reperfusion injury through the mitochondrial ATP-sensitive potassium channel

Previous clinical studies have shown that anisodamine could improve no-reflow phenomenon and prevent reperfusion arrhythmias, but whether this protective effect is related to the antagonism of the M-type cholinergic receptor or other potential mechanisms is uncertain. The aim of the present study was to investigate the role of the mitochondrial ATP-sensitive potassium channel (mitoK ATP ) in cardioprotective effect of anisodamine against ischemia/reperfusion injury. Anisodamine and 5- hydroxydecanoic acid were used to explore the relationship between anisodamine and mitoK ATP . Using a Langendorff isolated heart ischemia/reperfusion injury model, hemodynamic parameters and reperfusion ventricular arrhythmia were evaluated; in addition, changes in myocardial infarct size, cTnI from coronary effluent and myocardial ultrastructure, as well as ATP, MDA and SOD in myocardial tissues, were detected. In the hypoxia/reoxygenation injury model of neonatal rat cardiomyocyte, cTnI release in the culture medium and levels of ATP, MDA and SOD in cardiomyocytes and mitochondrial membrane potential, were analyzed. Overall, anisodamine could significantly improve the hemodynamic indexes of isolated rat heart injured by ischemia/reperfusion, reduce the occurrence of ventricular reperfusion arrhythmia and myocardial infarction area, and improve the ultrastructural damage of myocardium and mitochondria. The in vitro results demonstrated that anisodamine could improve mitochondrial energy metabolism, reduce oxidative stress and stabilize mitochondrial membrane potential. The cardioprotective effects were significantly inhibited by 5-hydroxydecanoic acid. In conclusion, this study suggests that the opening of mitoK ATP could play an important role in the protective effect of anisodamine against myocardial ischemia/reperfusion injury.

Targeting the Endothelium to Achieve Cardioprotection

Despite considerable improvements in the treatment of myocardial infarction, it is still a highly prevalent disease worldwide. Novel therapeutic strategies to limit infarct size are required to protect myocardial function and thus, avoid heart failure progression. Cardioprotection is a research topic with significant achievements in the context of basic science. However, translation of the beneficial effects of protective approaches from bench to bedside has proven difficult. Therefore, there is still an unmet need to study new avenues leading to protecting the myocardium against infarction. In line with this, the endothelium is an essential component of the cardiovascular system with multiple therapeutic targets with cardioprotective potential. Endothelial cells are the most abundant non-myocyte cell type in the heart and are key players in cardiovascular physiology and pathophysiology. These cells can regulate vascular tone, angiogenesis, hemostasis, and inflammation. Accordingly, endothelial dysfunction plays a fundamental role in cardiovascular diseases, which may ultimately lead to myocardial infarction. The endothelium is of paramount importance to protect the myocardium from ischemia/reperfusion injury via conditioning strategies or cardioprotective drugs. This review will provide updated information on the most promising therapeutic agents and protective approaches targeting endothelial cells in the context of myocardial infarction.

Reduced effect of ischemic preconditioning against endothelial ischemia-reperfusion injury with cardiovascular risk factors in humans

The extent that clustered CVD risk factors interfere with ischemic preconditioning (IPC) to protect against microvascular endothelial dysfunction with ischemia-reperfusion (I/R) injury in humans is unclear. We hypothesized that adults with a clustered burden of ≥3 CVD risk factors would demonstrate a reduced capacity of IPC to protect endothelial function with I/R injury. Twenty-two (age: 45 ± 14 year) adults [12 healthy controls; 10 raised risk (10-year FRS risk score ~3%)] were studied using a 2 × 2 randomized cross-over design. Pulse arterial tonometry was used to assess microvascular endothelium-dependent vasodilation during reactive hyperemia in response to endothelial I/R injury (20 min brachial artery occlusion/45 min reperfusion) that was preceded by remote IPC (3 × 5 min ischemia/reperfusion) or mock IPC. In both groups, microvascular reactive hyperemia was reduced ~20% (both P < 0.01) after endothelial I/R injury without remote IPC. However, in control subjects remote IPC prevented endothelial I/R injury (from baseline reactive hyperemic ratio: 2.1 ± 0.4 AU to post I/R injury: 2.5 ± 0.5 AU; P = 0.09). In contrast, the reactive hyperemia ratio in raised risk subjects was significantly reduced from 2.2 ± 0.6 AU to 1.9 ± 0.5 AU (P = 0.0087) despite attempts to induce protection by remote IPC, with the magnitude of reduction similar to their mock IPC trial. The magnitude of remote IPC-mediated endothelial protection against I/R injury was inversely related to the number of risk factors. CVD risk factors diminish the effect of IPC to protect the microvasculature from I/R injury in humans. Translating IPC to clinical practice for vasculoprotection will continue to be challenging in patients with increased CVD risk.

Improved endothelial-dependent and endothelial-independent skin vasodilator responses following remote ischemic preconditioning

One week of daily remote ischemic preconditioning (RIPC) improves cutaneous vasodilatory (VD) function. However, the underlying mechanisms and the number of sessions needed to optimize this adaptive response remain unclear. We hypothesized that the responses to localized heating of the skin will be greater after 2 wk as opposed to 1 wk of RIPC. Furthermore, 2 wk of repeated RIPC will augment cutaneous VD responses to thermal and pharmacological stimuli. In methods, twenty-four participants (24 ± 2 yr; 13 men, 11 women) performed repeated RIPC (7 daily sessions over 1 wk, n = 11; 12 sessions over 2 wk, n = 13), consisting of four repetitions of 5 min of arm blood flow occlusion separated by 5 min reperfusion. Laser speckle contrast imaging was used to measure skin blood flow responses, in perfusion units (PU), to local heating (T_loc = 42°C), acetylcholine (ACh), and sodium nitroprusside (SNP) before and after repeated RIPC. Data were expressed as cutaneous vascular conductance (CVC, in PU/mmHg). In results, the VD response to local heating increased after RIPC (∆CVC from baseline; 1 wk: 0.94 ± 0.11 to 1.19 ± 0.15, 2 wk: 1.18 ± 0.07 to 1.33 ± 0.10 PU/mmHg; P < 0.05) but the ∆CVC did not differ between weeks. SNP-induced VD increased after 2 wk of RIPC (∆CVC; 0.34 ± 0.07 to 0.63 ± 0.11 PU/mmHg; P < 0.05), but ACh-induced VD did not. In conclusion, repeated RIPC improves local heating- and SNP-mediated cutaneous VD. When compared with 1 wk of RIPC, 2 wk of RIPC does not induce further improvements in cutaneous VD function.NEW & NOTEWORTHY Repeated RIPC increases the cutaneous vasodilatory response to local heating and to sodium nitroprusside but not to acetylcholine. Thus, endothelial-independent and local heating-mediated cutaneous vasodilation are improved following RIPC. However, 2 wk of RIPC sessions are not more effective than 1 wk of RIPC sessions in enhancing local heating-mediated cutaneous vasodilation.

Hypoxic preconditioning improves the survival and neural effects of transplanted mesenchymal stem cells via CXCL12/CXCR4 signalling in a rat model of cerebral infarction

The treatment of neural deficiency after cerebral infarction is challenging, with limited therapeutic options. The transplantation of mesenchymal stem cells (MSCs) to the ischemic penumbra is a potential therapeutic approach. In the present study, a cerebral infarction model was generated by performing middle cerebral artery occlusion (MCAO) in SD rats. The expression of CXCR4 increased, and the number of MSCs migrating to the peri-infarct area was higher in rats transplanted with preconditioned MSCs than in rats transplanted with untreated MSCs. The rate of apoptosis, as evaluated by TUNEL staining and immunoblotting assays, was reduced in rats receiving preconditioned MSCs. A significant amelioration of neural regeneration and improved neurological function were observed in rats injected with preconditioned MSCs compared with those injected with untreated MSCs. However, the application of an siRNA targeting CXCL12 significantly inhibited the protective role of preconditioned MSCs against apoptosis and promoted the migration of MSCs to the ischemic area, leading to impaired neuronal regeneration and limited recovery of neuronal function. Hypoxic preconditioning of MSCs prior to transplantation suppressed apoptosis and increased their migration abilities, leading to the promotion of neuronal regeneration and improvement in neural function after transplantation. This preconditioning strategy may be considered as a potential approach for the modification of MSCs prior to cell transplantation therapy in patients with cerebral infarction. SIGNIFICANCE OF THE STUDY: We found that hypoxic preconditioning of MSCs improved their ability to promote neuronal regeneration and the recovery of neuronal function. Moreover, we showed that CXCR4 inhibited apoptosis, improved cell homing, and promoted neuronal differentiation, without influencing angiogenesis. Our study provides a relatively safe preconditioning method for potential use for cell transplantation therapy in ischemic cerebral infarction. The results presented here will facilitate the development of novel strategies and techniques to improve the tolerance and migration ability of transplanted cells for the treatment of cerebral infarction sequelae.

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.

Gap junctions in liver disease: Implications for pathogenesis and therapy

In the normal liver, cells interact closely through gap junctions. By providing a pathway for the trafficking of low molecular mass molecules, these channels contribute to tissue homeostasis and maintenance of hepatic function. Thus, dysfunction of gap junctions affects a wide variety of liver processes, such as differentiation, cell death, inflammation and fibrosis. In fact, dysfunctional gap junctions have been implicated, for more than a decade, in cholestatic disease, hepatic cancer and cirrhosis. Additionally, in recent years there is an increasing body of evidence that these channels are also involved in other relevant and prevalent liver pathological processes, such as non-alcoholic fatty liver disease, acute liver injury and portal hypertension. In parallel to these new clinical implications the available data include controversial observations. Thus, a comprehensive overview is required to better understand the functional complexity of these pores. This paper will review the most recent knowledge concerning gap junction dysfunction, with a special focus on the role of these channels in the pathogenesis of relevant clinical entities and on potential therapeutic targets that are amenable to modification by drugs.

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

KEY POINTS

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

ABSTRACT

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

Mechanisms involved in adenosine pharmacological preconditioning-induced cardioprotection

Adenosine is a naturally occurring breakdown product of adenosine triphosphate and plays an important role in different physiological and pathological conditions. Adenosine also serves as an important trigger in ischemic and remote preconditioning and its release may impart cardioprotection. Exogenous administration of adenosine in the form of adenosine preconditioning may also protect heart from ischemia-reperfusion injury. Endogenous release of adenosine during ischemic/remote preconditioning or exogenous adenosine during pharmacological preconditioning activates adenosine receptors to activate plethora of mechanisms, which either independently or in association with one another may confer cardioprotection during ischemia-reperfusion injury. These mechanisms include activation of K_ATP channels, an increase in the levels of antioxidant enzymes, functional interaction with opioid receptors; increase in nitric oxide production; decrease in inflammation; activation of transient receptor potential vanilloid (TRPV) channels; activation of kinases such as protein kinase B (Akt), protein kinase C, tyrosine kinase, mitogen activated protein (MAP) kinases such as ERK 1/2, p38 MAP kinases and MAP kinase kinase (MEK 1) MMP. The present review discusses the role and mechanisms involved in adenosine preconditioning-induced cardioprotection.

Unraveling the role of adenosine in remote ischemic preconditioning-induced cardioprotection

Remote ischemic preconditioning (RIPC) induced by alternate cycles of preconditioning ischemia and reperfusion protects the heart against sustained ischemia-reperfusion-induced injury. This technique has been translated to clinical levels in patients undergoing various surgical interventions including coronary artery bypass graft surgery, abdominal aortic aneurysm repair, percutaneous coronary intervention and heart valve surgery. Adenosine is a master regulator of energy metabolism and reduces myocardial ischemia-reperfusion-induced injury. Furthermore, adenosine is a critical trigger as well as a mediator in RIPC-induced cardioprotection and scientists have demonstrated the role of adenosine by showing an increase in its levels in the systemic circulation during RIPC delivery. Furthermore, the blockade of cardioprotective effects of RIPC in the presence of specific adenosine receptor blockers and transgenic animals with targeted ablation of A1 receptors has also demonstrated its critical role in RIPC. The studies have shown that adenosine may elicit cardioprotection via activation of neurogenic pathway. The present review describes the possible role and mechanism of adenosine in mediating RIPC-induced cardioprotection.