Exploring the Role of TRPV and CGRP in Adenosine Preconditioning and Remote Hind Limb Preconditioning-Induced Cardioprotection in Rats

Hydrogen sulfide restores cardioprotective effects of remote ischemic preconditioning in aged rats via HIF-1α/Nrf2 signaling pathway

The present study explored the therapeutic potential of hydrogen sulfide (H₂S) in restoring aging-induced loss of cardioprotective effect of remote ischemic preconditioning (RIPC) along with the involvement of signaling pathways. The left hind limb was subjected to four short cycles of ischemia and reperfusion (IR) in young and aged male rats to induce RIPC. The hearts were subjected to IR injury on the Langendorff apparatus after 24 h of RIPC. The measurement of lactate dehydrogenase, creatine kinase and cardiac troponin served to assess the myocardial injury. The levels of H₂S, cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), nuclear factor erythroid 2-related factor 2 (Nrf2), and hypoxia-inducible factor (HIF-1α) were also measured. There was a decrease in cardioprotection in RIPC-subjected old rats in comparison to young rats along with a reduction in the myocardial levels of H₂S, CBS, CSE, HIF-1α, and nuclear: cytoplasmic Nrf2 ratio. Supplementation with sodium hydrogen sulfide (NaHS, an H₂S donor) and l-cysteine (H₂S precursor) restored the cardioprotective actions of RIPC in old hearts. It increased the levels of H₂S, HIF-1α, and Nrf2 ratio without affecting CBS and CSE. YC-1 (HIF-1α antagonist) abolished the effects of NaHS and l-cysteine in RIPC-subjected old rats by decreasing the Nrf2 ratio and HIF-1α levels, without altering H₂S.The late phase of cardioprotection of RIPC involves an increase in the activity of H₂S biosynthetic enzymes, which increases the levels of H₂S to upregulate HIF-1α and Nrf2. H₂S has the potential to restore aging-induced loss of cardioprotective effects of RIPC by upregulating HIF-1α/Nrf2 signaling.

Exploring the role of neurogenic pathway-linked cholecystokinin release in remote preconditioning-induced cardioprotection

Purpose:

The current study explored the involvement of neurogenic pathway-linked cholecystokinin (CCK) release in RIP-induced cardioprotection in rats.

Methods:

Male Wistar rats were subjected to four cycles of alternate episodes of ischemia and reperfusion (five min each) to induce RIP. Thereafter, the hearts were subjected to global ischemia and reperfusion ex vivo. The myocardial damage was assessed by quantifying the levels of heartspecific biochemicals i.e. LDH-1, CK-MB and cTnT. Apoptotic cell injury was assessed by measuring the levels of caspase-3 and Bcl-2. The levels of CCK were measured in the plasma following RIP.

Results:

Exposure to RIP significantly increased the plasma levels of CCK and attenuated IR-induced myocardial injury. Administration of CCK antagonist, proglumide significantly attenuated RIP-induced cardioprotection. Administration of hexamethonium, a ganglion blocker, abolished RIP-induced increase in plasma CCK levels and cardioprotective effects. Exogenous delivery of CCK-8 restored the effects of RIP in hexamethonium treated animals.

Conclusion:

RIP activates the neurogenic pathway that may increase the plasma levels of CCK, which may act on the heart-localized CCK receptors to produce cardioprotection against I/R injury.

Remote ischemic preconditioning reduces myocardial ischemia-reperfusion injury through unacylated ghrelin-induced activation of the JAK/STAT pathway

Remote ischemic preconditioning (RIPC) offers cardioprotection against myocardial ischemia-reperfusion injury. The humoral factors involved in RIPC that are released from parasympathetically innervated organs have not been identified. Previous studies showed that ghrelin, a hormone released from the stomach, is associated with cardioprotection. However, it is unknown whether or not ghrelin is involved in the mechanism of RIPC. This study aimed to determine whether ghrelin serves as one of the humoral factors in RIPC. RIPC group rats were subjected to three cycles of ischemia and reperfusion for 5 min in two limbs before left anterior descending (LAD) coronary artery ligation. Unacylated ghrelin (UAG) group rats were given 0.5 mcg/kg UAG intravenously 30 min before LAD ligation. Plasma levels of UAG in all groups were measured before and after RIPC procedures and UAG administration. Additionally, JAK2/STAT3 pathway inhibitor (AG490) was injected in RIPC and UAG groups to investigate abolishment of the cardioprotection of RIPC and UAG. Plasma levels of UAG, infarct size and phosphorylation of STAT3 were compared in all groups. Infarct size was significantly reduced in RIPC and UAG groups, compared to the other groups. Plasma levels of UAG in RIPC and UAG groups were significantly increased after RIPC and UAG administration, respectively. The cardioprotective effects of RIPC and UAG were accompanied by an increase in phosphorylation of STAT3 and abolished by AG490. This study indicated that RIPC reduces myocardial ischemia and reperfusion injury through UAG-induced activation of JAK/STAT pathway. UAG may be one of the humoral factors involved in the cardioprotective effects of RIPC.

Effect of Remote Ischemic Conditioning in Patients With Takotsubo Syndrome After Acute Stroke: Study Protocol for a Randomized Controlled Trial

Introduction: Takotsubo syndrome (TTS) is an acute heart failure syndrome which is preceded by a variety of emotional or physical triggers, with central nervous system conditions being an important trigger. Remote ischemic conditioning (RIC) is a promising interventional treatment based on the probability that both TTS and acute coronary syndrome may respond similarly to interventions. The heart protection effect of RIC has been repeatedly confirmed in animal models and observational clinical trials; however, it has never been studied in patients with TTS after acute stroke in randomized clinical trials with a higher level of evidence. The present study will be a proof-of-concept study to determine whether RIC can reduce cardiac injury and eventually improve the heart function and clinical outcomes of TTS patients after acute stroke. Methods and Analysis: A single-center, outcome-assessor-blinded, randomized controlled trial (RCT) will be conducted to evaluate the effect of RIC in TTS patients after acute stroke. Major eligibility criteria include TTS patients diagnosed with acute stroke, which can be confirmed on computed tomography or magnetic resonance imaging; patients aged 18-75 years; patients admitted to a hospital within 48 h after the onset of acute stroke; and patients diagnosed with Takotsubo cardiomyopathy with an InterTAK diagnostic score ≥50. A total of 60 eligible patients will be randomly allocated into either the RIC or the control group. The primary endpoint is a composite of death from any cause and major adverse cardiac and cerebrovascular events during the in-hospital period and at the 1- and 6-month follow-up. Ethics and dissemination: This study has been approved by the Medical Ethics Committee of Xuanwu Hospital, Capital Medical University ([2017] 072). The study findings will be presented at international conferences and published in a peer-reviewed journal. Trial registration: This study has been prospectively registered in the Chinese Clinical Trial Registry on September 10, 2018 (ChiCTR1800018290).

LncRNA 1700020I14Rik/miR-297a/CGRP axis suppresses myocardial cell apoptosis in myocardial ischemia-reperfusion injury

BACKGROUND

Long non-coding RNAs (lncRNAs) are closely related to various human diseases, but their role in myocardial injury has not been fully elucidated. In the current study, we found that the expression of lncRNA 1700020I14Rik was significantly down-regulated in myocardial injury tissues and the underlying mechanism by which lncRNA 1700020I14Rik regulated myocardial cell injury was investigated.

METHODS

The model of myocardial ischemia-reperfusion (I/R) injury and myocardial cells hypoxia/reoxygenation (H/R) injury were established and the expression of 1700020I14Rik, miR-297a or CGRP was analyzed by qRT-PCR or Western blot. Moreover, myocardial cell apoptosis was assessed by TUNEL staining and the concentration of LDH in the mouse plasma sample or myocardial cell culture supernatant was measured by the LDH cytotoxicity test kit. Furthermore, the differences of myocardial cell survival rate after H/R treatment were assessed by MTT assay and the observation of CGRP expression was performed in HL-1 cells overexpressed or silenced with 1700020I14Rik or miR-297a. In addition, the regulating function of miR-297a on 1700020I14Rik and CGRP expression was analyzed by a dual luciferase reporter assay.

RESULTS

The expressions of 1700020I14Rik and CGRP were abnormally down-regulated in a model of myocardial I/R injury and myocardial cells H/R injury, while miR-297a was up-regulated. By TUNEL staining, the apoptotic rate of myocardial cells in the model of myocardial I/R injury was significantly increased. Furthermore, the concentrations of LDH in the mouse plasma sample or myocardial cell culture supernatant were significantly increased after myocardial cell injury. By MTT assay, the survival rate of cells was decreased after myocardial cells were treated with H/R. In addition, overexpression of 1700020I14Rik or knockdown of miR-297a could up-regulate CGRP protein level, while interference with 1700020I14Rik or overexpression of miR-297a produced the opposite result. Further study confirmed that lncRNA 1700020I14Rik/miR-297a/CGRP axis suppressed myocardial cell apoptosis in myocardial I/R injury.

CONCLUSION

Our results indicated that 1700020I14Rik was abnormally down-regulated in myocardial injury tissues. In-depth studies manifested that 1700020I14Rik/miR-297a/CGRP axis suppressed myocardial cell apoptosis in myocardial I/R injury.

Late Phases of Cardioprotection During Remote Ischemic Preconditioning and Adenosine Preconditioning Involve Activation of Neurogenic Pathway

BACKGROUND

The role of the neurogenic pathway in early phases of cardioprotection during remote ischemic preconditioning (RIPC) and adenosine preconditioning is reported.

AIM

This study was designed to explore the involvement of the neurogenic pathway in late phases of cardioprotection during RIPC and adenosine preconditioning.

MATERIAL AND METHODS

Fifty-four Wistar rats were used and divided into 9 experimental groups. RIPC was induced by tying the blood pressure cuff around the hind limb and subjecting to 4 cycles of inflation and deflation of 5 minutes each. In early RIPC, the heart was isolated immediately after the last episode of RIPC, whereas in late RIPC, the heart was isolated 24 hours after the last cycle of RIPC. In a similar way, adenosine preconditioning was instituted in early and late phases by either isolating the heart 40 minutes or 24 hours after adenosine (4 mg/kg, intraperitoneally [i.p.]) administration. Isolated hearts were subjected to ischemia-reperfusion (I/R) injury on the Langendorff's system.

RESULTS

Both early and late phases of RIPC and adenosine preconditioning significantly abrogated I/R-induced myocardial injury in terms of decrease in the release of lactate dehydrogenase, creatine kinase, and decrease in infarct size. Pretreatment with hexamethonium, a ganglion blocker (20 mg/kg, i.p.), significantly abolished the cardioprotective effects of both early and late phases of RIPC and adenosine preconditioning.

CONCLUSION

Apart from the involvement of the neurogenic pathway in the early phases, there is a critical role of the neurogenic pathway in the late phase of cardioprotection during RIPC and adenosine preconditioning.

A Review of Humoral Factors in Remote Preconditioning of the Heart

A humoral mechanism of cardioprotection by remote ischemic preconditioning (RIP) has been clearly demonstrated in various models of ischemia-reperfusion including upper and lower extremities, liver, and the mesenteric and renal arteries. A wide range of humoral factors for RIP have been proposed including hydrophobic peptides, opioid peptides, adenosine, prostanoids, endovanilloids, endocannabinoids, calcitonin gene-related peptide, leukotrienes, noradrenaline, adrenomedullin, erythropoietin, apolipoprotein, A-I glucagon-like peptide-1, interleukin 10, stromal cell-derived factor 1, and microRNAs. Virtually, all of the components of ischemic preconditioning's signaling pathway such as nitric oxide synthase, protein kinase C, redox signaling, PI3-kinase/Akt, glycogen synthase kinase β, ERK1/2, mitoK_ATP channels, Connexin 43, and STAT were all found to play a role. The signaling pattern also depends on which remote vascular bed was subjected to ischemia and on the time between applying the rip and myocardial ischemia occurs. Because there is convincing evidence for many seemingly diverse humoral components in RIP, the most likely explanation is that the overall mechanism is complex like that seen in ischemic preconditioning where multiple components are both in series and in parallel and interact with each other. Inhibition of any single component in the right circumstance may block the resulting protective effect, and selectively activating that component may trigger the protection. Identifying the humoral factors responsible for RIP might be useful in developing drugs that confer RIP's protection in a more comfortable and reliable manner.

The Role of Calcitonin Gene Related Peptide (CGRP) in Neurogenic Vasodilation and Its Cardioprotective Effects

Calcitonin gene-related peptide (CGRP) is a highly potent vasoactive peptide released from sensory nerves, which is now proposed to have protective effects in several cardiovascular diseases. The major α-form is produced from alternate splicing and processing of the calcitonin gene. The CGRP receptor is a complex composed of calcitonin like receptor (CLR) and a single transmembrane protein, RAMP1. CGRP is a potent vasodilator and proposed to have protective effects in several cardiovascular diseases. CGRP has a proven role in migraine and selective antagonists and antibodies are now reaching the clinic for treatment of migraine. These clinical trials with antagonists and antibodies indicate that CGRP does not play an obvious role in the physiological control of human blood pressure. This review discusses the vasodilator and hypotensive effects of CGRP and the role of CGRP in mediating cardioprotective effects in various cardiovascular models and disorders. In models of hypertension, CGRP protects against the onset and progression of hypertensive states by potentially counteracting against the pro-hypertensive systems such as the renin-angiotensin-aldosterone system (RAAS) and the sympathetic system. With regards to its cardioprotective effects in conditions such as heart failure and ischaemia, CGRP-containing nerves innervate throughout cardiac tissue and the vasculature, where evidence shows this peptide alleviates various aspects of their pathophysiology, including cardiac hypertrophy, reperfusion injury, cardiac inflammation, and apoptosis. Hence, CGRP has been suggested as a cardioprotective, endogenous mediator released under stress to help preserve cardiovascular function. With the recent developments of various CGRP-targeted pharmacotherapies, in the form of CGRP antibodies/antagonists as well as a CGRP analog, this review provides a summary and a discussion of the most recent basic science and clinical findings, initiating a discussion on the future of CGRP as a novel target in various cardiovascular diseases.

Exploring the putative role of TRPV1 -dependent CGRP release in remote hind preconditioning-induced cardioprotection

BACKGROUND

Remote ischemic preconditioning (RIPC) is a phenomenon whereby transient nonlethal ischemia and reperfusion episodes confer protection against prolonged ischemia reperfusion-induced injury. However, the underlying intracellular signaling has not been extensively explored.

OBJECTIVE

This study aimed to inspect the putative involvement of TRPV₁ -dependent CGRP release in mediating remote hind limb preconditioning-induced cardioprotection.

METHODS

In this study, remote hind limb preconditioning stimulus was delivered (four consecutive episodes of 5 minutes of ischemia reperfusion) using a blood pressure cuff tied at the inguinal level of the rat. The isolated rat hearts were perfused on the Langendorff's system and were subjected to 30-minutes global ischemia and 120-minutes reperfusion. Prolonged ischemia and subsequent reperfusion led to myocardial injury that was evaluated in terms of infarct size, LDH release, CK release, LVDP, +dp/dt_max , -dp/dt_min , and coronary flow rate. The pharmacological agents used in this study included capsaicin as TRPV₁ channel activator, sumatriptan and CGRP8-37 as CGRP blockers.

RESULTS

Remote hind limb and capsaicin preconditioning (10 mg/kg^-1 ) significantly reduced the infarct size, LDH release, CK release and significantly improved LVDP, +dp/dt_max , -dp/dt_min , and coronary flow rate. However, remote hind limb and capsaicin preconditioning-induced cardioprotective effects were remarkably reduced in the presence of sumatriptan (8 mg/kg^-1 ) and CGRP8-37 (1 mg/kg^-1 ).

CONCLUSION

This indicates that remote hind limb preconditioning stimulus probably activates TRPV₁ channels which subsequently induces CGRP release to produce cardioprotective effects.

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.

Investigating the possible mechanisms involved in adenosine preconditioning-induced cardioprotection in rats

BACKGROUND

Adenosine is a breakdown product of adenosine triphosphate and plays an important role in pharmacological preconditioning. The cardioprotective effects of adenosine preconditioning are well established. However, the possible mechanisms need to be explored.

AIM

This study was aimed to investigate the possible mechanisms involved in adenosine preconditioning-induced cardioprotection in rats.

METHODS

Rat heart was isolated and perfused on Langendorff apparatus. Global ischemia for 30 minutes followed by reperfusion for 120 minutes was employed to produce myocardial injury. Myocardial injury was assessed by measuring myocardial infarct size, release of lactate dehydrogenase (LDH) and creatine kinase (CK) in the coronary effluent and hemodynamic parameters including left ventricular developed pressure (LVDP), dp/dt_max, and dp/dt_min . Serum nitrite levels were measured as an index of nitric oxide release in blood.

RESULTS

Adenosine (4 mg/kg) preconditioning significantly decreased ischemia-reperfusion-induced increase in LDH, CK release, infarct size, improved LVDP, dp/dt_max and dp/dt_min, and increased serum nitrite levels. Pretreatment with L-NAME, a specific NOS inhibitor, (5 mg/kg) and montelukast, leukotriene receptor antagonist, (10 mg/kg) significantly abrogated the cardioprotective effect of adenosine preconditioning. However, seratrodast, thromboxane A₂ antagonist, (15 mg/kg) had no effect on adenosine-induced cardioprotection. Sodium nitroprusside (SNP) preconditioning also produced cardioprotective effects. However, caffeine (20 mg/kg) (adenosine receptor blocker) and seratrodast (15 mg/kg) had no effect on SNP-induced cardioprotection. Administration of montelukast abrogated the cardioprotective effects of SNP preconditioning-induced cardioprotection.

CONCLUSION

Adenosine preconditioning may increase the release of nitric oxide, which in turn may increase the release of cysteinyl leukotrienes to confer cardioprotection.

Cardioprotective Exercise and Pharmacologic Interventions as Complementary Antidotes to Cardiovascular Disease

Exercise and pharmacologic therapies to prevent and treat cardiovascular disease have advanced largely through independent efforts. Understanding of first-line drug therapies, findings from preclinical animal studies, and the need for research initiatives related to complementary cardioprotective exercise-pharma interventions are reviewed from the premise that contemporary cardioprotective therapies must include adjunctive exercise and lifestyle interventions in addition to pharmacologic agents.