Bradykinin in ischemic conditioning-induced tissue protection: Evidences and possible mechanisms

Neuropeptides: Potential neuroprotective agents in ischemic injury

AIM

Ischemic damage to the brain is linked to an increased rate of morbidity and mortality worldwide. In certain parts of the world, it remains a leading cause of mortality and the primary cause of long-term impairment. Ischemic injury is exacerbated when particular neuropeptides are removed, or their function in the brain is blocked, whereas supplying such neuropeptides lowers ischemic harm. Here, we have discussed the role of neuropeptides in ischemic injury.

MATERIALS & METHODS

Numerous neuropeptides had their overexpression following cerebral ischemia. Neuropeptides such as NPY, CGRP, CART, SP, BK, PACAP, oxytocin, nociception, neurotensin and opioid peptides act as transmitters, documented in several "in vivo" and "in vitro" studies. Neuropeptides provide neuroprotection by activating the survival pathways or inhibiting the death pathways, i.e., MAPK, BDNF, Nitric Oxide, PI3k/Akt and NF-κB.

KEY FINDINGS

Neuropeptides have numerous beneficial effects in ischemic models, including antiapoptotic, anti-inflammatory, and antioxidant actions that provide a powerful protective impact in neurons when combined. These innovative therapeutic substances have the potential to treat ischemia injury due to their pleiotropic modes of action.

SIGNIFICANCE

This review emphasizes the neuroprotective role of neuropeptides in ischemic injury via modulation of various signalling pathways i.e., MAPK, BDNF, Nitric Oxide, PI3k/Akt and NF-κB.

Dexmedetomidine protects the heart against ischemia reperfusion injury via regulation of the bradykinin receptors

BACKGROUND

Dexmedetomidine (DEX) has been reported to protect the heart against ischemia reperfusion (I/R) injury. However, the exact mechanisms are still not fully understood.

METHODS AND RESULTS

A rat cardiac I/R injury model was induced by ligation of the left anterior descending coronary artery for 1 h and subsequent reperfusion for 2 h, and DEX was administered intravenously 30 min before ischemia. We confirmed that DEX treatment mitigated cardiac I/R injury. Interestingly, we found that DEX regulated the expression of bradykinin (BK) receptors (B1R and B2R) in rat hearts during I/R injury and enhanced the protective action of BK administered during reperfusion. Moreover, in vitro hypoxia reoxygenation (H/R) injury was induced in neonatal rat cardiomyocytes (CMs), and DEX was administered 1 h before hypoxia. The in vitro findings were consistent with the in vivo experiments. We found that an α2-adrenoceptor (α2-AR) antagonist (yohimbine) completely aborted DEX-induced B1R and B2R regulation; an adenylyl cyclase (AC) agonist (forskolin) blocked B1R downregulation, while a phosphatidylinositol 3-kinase (PI3K) inhibitor (LY294002) blocked B2R upregulation. The above findings indicated that DEX interacted with α2-AR in cardiomyocytes, inhibited B1R expression via suppression of AC, and stimulated B2R expression via activation of PI3K.

CONCLUSIONS

DEX regulates BK receptor expression and potentiates the protection of BK in cardiac I/R injury, which suggests that modulating endogenous cardioprotective factors may play an important role in DEX-induced cardioprotection.

Nonclassical Axis of the Renin-Angiotensin System and Neprilysin: Key Mediators That Underlie the Cardioprotective Effect of PPAR-Alpha Activation during Myocardial Ischemia in a Metabolic Syndrome Model

The activation of the renin-angiotensin system (RAS) participates in the development of metabolic syndrome (MetS) and in heart failure. PPAR-alpha activation by fenofibrate reverts some of the effects caused by these pathologies. Recently, nonclassical RAS components have been implicated in the pathogenesis of hypertension and myocardial dysfunction; however, their cardiac functions are still controversial. We evaluated if the nonclassical RAS signaling pathways, directed by angiotensin III and angiotensin-(1-7), are involved in the cardioprotective effect of fenofibrate during ischemia in MetS rats. Control (CT) and MetS rats were divided into the following groups: (a) sham, (b) vehicle-treated myocardial infarction (MI-V), and (c) fenofibrate-treated myocardial infarction (MI-F). Angiotensin III and angiotensin IV levels and insulin increased the aminopeptidase (IRAP) expression and decreased the angiotensin-converting enzyme 2 (ACE2) expression in the hearts from MetS rats. Ischemia activated the angiotensin-converting enzyme (ACE)/angiotensin II/angiotensin receptor 1 (AT1R) and angiotensin III/angiotensin IV/angiotensin receptor 4 (AT4R)-IRAP axes. Fenofibrate treatment prevented the damage due to ischemia in MetS rats by favoring the angiotensin-(1-7)/angiotensin receptor 2 (AT2R) axis and inhibiting the angiotensin III/angiotensin IV/AT4R-IRAP signaling pathway. Additionally, fenofibrate downregulated neprilysin expression and increased bradykinin production. These effects of PPAR-alpha activation were accompanied by a reduction in the size of the myocardial infarct and in the activity of serum creatine kinase. Thus, the regulation of the nonclassical axis of RAS forms part of a novel protective effect of fenofibrate in myocardial ischemia.

Anti-Hypertensive Effects of Peptides Derived from Rice Bran Protein

Hypertension is one of the major risk factors for arteriosclerosis. Anti-hypertensive peptides derived from animal proteins, such as milk, eggs and fish, are well studied. Anti-hypertensive peptides have also been identified from plant proteins such as soybeans. Rice bran, a byproduct of white rice polishing, is rich in protein and its high protein efficiency ratio is well known. This review discusses the anti-hypertensive peptides identified from rice bran protein and their mechanisms. In addition, we describe protease-digested rice bran from which functional peptides have not been isolated.

Autocrine Bradykinin Release Promotes Ischemic Preconditioning-Induced Cytoprotection in Bovine Aortic Endothelial Cells

The aims of this study were to assess whether ischemic preconditioning (PC) induces bradykinin (Bk) synthesis in bovine aortic endothelial cells (bAECs) and, if so, to explore the molecular mechanisms by which this peptide provides cytoprotection against hypoxia. PC was induced by exposing bAECs to three cycles of 15 min of hypoxia followed by 15 min of reoxygenation. Bk synthesis peaked in correspondence to the early and late phases of PC (10⁻¹² M and 10⁻¹¹ M, respectively) and was abolished by a selective tissue kallikrein inhibitor, aprotinin. Stimulation with exogenous Bk at concentrations of 10⁻¹² M and 10⁻¹¹ M reduced the cell death induced by 12 h of hypoxia by 50%. Pretreatment with HOE−140, a Bk receptor 2 (BKR2) inhibitor, in bAECs exposed to 12 h of hypoxia, abrogated the cytoprotective effect of early and late PC, whereas des-Arg-HOE-140, a Bk receptor 1 (BKR1) inhibitor, affected only the late PC. In addition, we found that PC evoked endocytosis and the recycling of BKR2 during both the early and late phases, and that inhibition of these pathways affected PC-mediated cytoprotection. Finally, we evaluated the activation of PKA and Akt in the presence or absence of BKR2 inhibitor. HOE-140 abrogated PKA and Akt activation during both early and late PC. Consistently, BKR2 inhibition abolished cross-talk between PKA and Akt in PC. In bAECs, Bk-synthesis evoked by PC mediates the protection against both apoptotic and necrotic hypoxia-induced cell death in an autocrine manner, by both BKR2- and BKR1-dependent mechanisms.

Effects of angiotensin-converting enzyme inhibitor/angiotensin receptor blocker use on cancer therapy-related cardiac dysfunction: a meta-analysis of randomized controlled trials

Angiotensin-converting enzyme inhibitor (ACEI) and angiotensin receptor blocker (ARB) may attenuate cancer therapy-related cardiac dysfunction (CTRCD). However, results of the previous studies were not consistent. We performed a meta-analysis to evaluate the influence of ACEI/ARB on CTRCD. Randomized controlled trials (RCTs) were obtained by searching of PubMed, Embase, and Cochrane's Library databases. A random-effect model was used to pool the results. Nine RCTs with 1095 cancer patients that underwent chemotherapy with anthracycline and/or trastuzumab were included. Using of ACEI/ARB significantly preserved left ventricular ejection fraction (LVEF, weighed mean difference = 4.24%, p = 0.002) compared with controls. Subgroup analyses showed that the benefits of ACEI/ARB on LVEF following chemotherapy were consistent and independent of study characteristics including study design, sample size, cancer type, chemotherapy protocols, preventative medications of ACEI or ARB, methods for LVEF measurement, and follow-up durations. The benefits on LVEF following chemotherapy were more remarkable in studies using ACEI and followed ≤ 12 months (p for subgroup difference = 0.04 and 0.02). Use of ACEI/ARB did not significantly reduce the risk of cardiotoxicity events (risk ratio [RR] = 0.63, p = 0.22) but increased the risk of hypotension in these patients (RR = 3.94, p = 0.008). These results indicated that using of ACEI/ARB may moderately attenuate CTRCD following chemotherapy with anthracycline and/or trastuzumab. Large-scale RCTs are needed to evaluate whether the benefits of ACEI/ARB on LVEF are clinically relevant.

Pain attenuating actions of vincristinet-preconditioning in chemotherapeutic agent-induced neuropathic pain: key involvement of T-type calcium channels

Preconditioning is a well-documented strategy that induces hepatic protection, renal protection, cardioprotection, and neuroprotection but its mechanism still remains to be elucidated. Hence, the present study investigated the protective mechanism underlying pain attenuating effects of vincristine-preconditioning in chemotherapeutic agent-induced neuropathic pain. Neuropathic pain was induced by administration of vincristine (50 µg/kg, i.p.) for 10 days in rats. Vincristine-preconditioning was induced by administration of vincristine (2, 5, and 10 µg/kg, i.p) for 5 days before administration of pain-inducing dose of vincristine (50 µg/kg, i.p.). Vincristine-preconditioning (10 µg/kg, i.p) for 5 days significantly reduced vincristine (50 µg/kg, i.p.) induced pain-related behaviors including paw cold allodynia, mechanical hyperalgesia, and heat hyperalgesia. However, vincristine (2 and 5 µg/kg, i.p) did not significantly ameliorate the vincristine (50 µg/kg, i.p.) induced neuropathic pain in rats. Furthermore, to explore the involvement of calcium channels in pain attenuating mechanism of vincristine-preconditioning, T-type calcium channel blocker, ethosuximide (100 and 200 mg/kg, i.p.) and L-type calcium channel blocker, amlodipine (5 and 10 mg/kg, i.p.) were used. Pretreatment with T-type calcium channel blocker, ethosuximide significantly abolished vincristine-preconditioning-induced protective effect. However, pretreatment with L-type calcium channel blocker, amlodipine did not alter vincristine-preconditioning-induced pain-related behaviors. This indicates that vincristine-preconditioning has protective effect on pain-related parameters due to opening of calcium channels, particularly T-type calcium channels that lead to entry of small magnitude of intracellular calcium through these channels and prevent the deleterious effects of high-dose vincristine.

Vasorelaxant and Antihypertensive Effects That Are Dependent on the Endothelial NO System Exhibited by Rice Bran-Derived Tripeptide

We recently identified a novel, potent antihypertensive peptide, Leu-Arg-Ala (LRA; minimum effective dose = 0.25 mg/kg), from rice bran protein. In this study, we found that LRA potently relaxed mesenteric arteries isolated from spontaneously hypertensive rats (SHRs) (EC₅₀ = 0.1 μM). In contrast, the vasorelaxant activity of each amino acid that constitutes the LRA tripeptide was remarkably attenuated. The LRA-induced vasorelaxant activity was inhibited by N(G)-nitro-l-arginine methyl ester (L-NAME; NO synthase [NOS] inhibitor) but not by an antagonist of bradykinin B2 and Mas receptors or by a phosphoinositide 3-kinase inhibitor. The antihypertensive effect induced after the oral administration of LRA was inhibited by L-NAME. LRA also induced the phosphorylation of endothelial NOS in human umbilical vein endothelial cells. Taken together, LRA may exhibit antihypertensive effects via NO-mediated vasorelaxation. LRA is the first example of a NO-dependent vasorelaxant peptide identified from rice bran protein.

Molecular features characterizing non-peptide selectivity to the human B1 and B2 bradykinin receptors

Bradykinin is produced in response to inflammation, trauma, burns, shock, allergy and some cardiovascular diseases. Actions of this peptide are mediated through two different G-protein coupled receptors, named B1 and B2 that have different pharmacological characteristics. The former is up-regulated during inflammation episodes or tissue trauma whereas, the latter is constitutively expressed in a variety of cell types. In a previous work we have characterized the molecular features that explain the observed structure-activity results for both receptors by means of molecular modeling studies, using diverse ligands for both receptors. These results were summarized in the form of two different pharmacophores that provided new insights to be used for the design of novel molecules with antagonistic profile. In the present work, we compare these pharmacophores to understand the features that characterize ligand selectivity to the two bradykinin receptors. The study shows that most of the residues involved in the binding pocket are similar in both receptors and consequently are the pharmacophores obtained. The main difference between the two pharmacophores remains on point #5 that involves a polar moiety for the B1 receptor and an aromatic ring for the B2 receptor. Accordingly, analysis of the prospective bound conformation of several non-selective small molecule ligands of the bradykinin receptors permits to conclude that fulfilment of point#5 is a requirement to produce selective ligands. However, the study also shows that this is a necessary condition only, since ligands need also to be bulky enough to avoid binding to these receptors in diverse poses. These results provide new insights for a better understanding of the molecular features that ligands are required to exhibit to be selective bradykinin ligands.

Limb Remote Ischemic Conditioning: Mechanisms, Anesthetics, and the Potential for Expanding Therapeutic Options

Novel and innovative approaches are essential in developing new treatments and improving clinical outcomes in patients with ischemic stroke. Remote ischemic conditioning (RIC) is a series of mechanical interruptions in blood flow of a distal organ, following end organ reperfusion, shown to significantly reduce infarct size through inhibition of oxidation and inflammation. Ischemia/reperfusion (I/R) is what ultimately leads to the irreversible brain damage and clinical picture seen in stroke patients. There have been several reports and reviews about the potential of RIC in acute ischemic stroke; however, the focus here is a comprehensive look at the differences in the three types of RIC (remote pre-, per-, and postconditioning). There are some limited uses of preconditioning in acute ischemic stroke due to the unpredictability of the ischemic event; however, it does provide the identification of biomarkers for clinical studies. Remote limb per- and postconditioning offer a more promising treatment during patient care as they can be harnessed during or after the initial ischemic insult. Though further research is needed, it is imperative to discuss the importance of preclinical data in understanding the methods and mechanisms involved in RIC. This understanding will facilitate translation to a clinically feasible paradigm for use in the hospital setting.

Extracts of Crataegus oxyacantha and Rosmarinus officinalis Attenuate Ischemic Myocardial Damage by Decreasing Oxidative Stress and Regulating the Production of Cardiac Vasoactive Agents

Numerous studies have supported a role for oxidative stress in the development of ischemic damage and endothelial dysfunction. Crataegus oxyacantha (Co) and Rosmarinus officinalis (Ro) extracts are polyphenolic-rich compounds that have proven to be efficient in the treatment of cardiovascular diseases. We studied the effect of extracts from Co and Ro on the myocardial damage associated with the oxidative status and to the production of different vasoactive agents. Rats were assigned to the following groups: (a) sham; (b) vehicle-treated myocardial infarction (MI) (MI-V); (c) Ro extract-treated myocardial infarction (MI-Ro); (d) Co extract-treated myocardial infarction (MI-Co); or (e) Ro+Co-treated myocardial infarction (MI-Ro+Co). Ro and Co treatments increased total antioxidant capacity, the expression of superoxide dismutase (SOD)-Cu2+/Zn2+, SOD-Mn2+, and catalase, with the subsequent decline of malondialdehyde and 8-hydroxy-2'-deoxyguanosine levels. The extracts diminished vasoconstrictor peptide levels (angiotensin II and endothelin-1), increased vasodilators agents (angiotensin 1-7 and bradikinin) and improved nitric oxide metabolism. Polyphenol treatment restored the left intraventricular pressure and cardiac mechanical work. We conclude that Ro and Co treatment attenuate morphological and functional ischemic-related changes by both an oxidant load reduction and improvement of the balance between vasoconstrictors and vasodilators.

Bradykinin regulates cell growth and migration in cultured human cardiac c-Kit+ progenitor cells

Bradykinin is a well-known endogenous vasoactive peptide. The present study investigated the bradykinin receptor expression in human cardiac c-Kit⁺ progenitor cells and the potential role of bradykinin in regulating cell cycling progression and mobility. It was found that mRNA and protein of bradykinin type 2 receptors, but not bradykinin type 1 receptors, were abundant in cultured human cardiac c-Kit⁺ progenitor cells. Bradykinin (1-10 nM) stimulated cell growth and migration in a concentration-dependent manner. The increase of cell proliferation was related to promoting G0/G1 transition into G2/M and S phase. Western blots revealed that bradykinin significantly increased pAkt and pERK1/2 as well as cyclin D1, which were countered by HOE140 (an antagonist of bradykinin type 2 receptors) or by silencing bradykinin type 2 receptors. The increase of pAkt, pERK1/2 and cyclin D1 by bradykinin was prevented by the PI3K inhibitor Ly294002, the PLC inhibitors U73122 and neomycin, and/or the PKC inhibitor chelerythrine and the MAPK inhibitor PD98059. Our results demonstrate the novel information that bradykinin promotes cell cycling progression and migration in human cardiac c-Kit⁺ progenitor cells via activating PI3K, PLC, PKC, cyclin D1, pERK1/2, and pAkt.

The mitochondrial permeability transition pore in AD 2016: An update

Over the past 30years the mitochondrial permeability transition - the permeabilization of the inner mitochondrial membrane due to the opening of a wide pore - has progressed from being considered a curious artifact induced in isolated mitochondria by Ca(2+) and phosphate to a key cell-death-inducing process in several major pathologies. Its relevance is by now universally acknowledged and a pharmacology targeting the phenomenon is being developed. The molecular nature of the pore remains to this day uncertain, but progress has recently been made with the identification of the FOF1 ATP synthase as the probable proteic substrate. Researchers sharing this conviction are however divided into two camps: these believing that only the ATP synthase dimers or oligomers can form the pore, presumably in the contact region between monomers, and those who consider that the ring-forming c subunits in the FO sector actually constitute the walls of the pore. The latest development is the emergence of a new candidate: Spastic Paraplegia 7 (SPG7), a mitochondrial AAA-type membrane protease which forms a 6-stave barrel. This review summarizes recent developments of research on the pathophysiological relevance and on the molecular nature of the mitochondrial permeability transition pore. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

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.