Investigating the involvement of glycogen synthase kinase-3β and gap junction signaling in TRPV1 and remote hind preconditioning-induced cardioprotection

Impact of Maturation on Myocardial Response to Ischemia and the Effectiveness of Remote Preconditioning in Male Rats

Aging attenuates cardiac tolerance to ischemia/reperfusion (I/R) associated with defects in protective cell signaling, however, the onset of this phenotype has not been completely investigated. This study aimed to compare changes in response to I/R and the effects of remote ischemic preconditioning (RIPC) in the hearts of younger adult (3 months) and mature adult (6 months) male Wistar rats, with changes in selected proteins of protective signaling. Langendorff-perfused hearts were exposed to 30 min I/120 min R without or with prior three cycles of RIPC (pressure cuff inflation/deflation on the hind limb). Infarct size (IS), incidence of ventricular arrhythmias and recovery of contractile function (LVDP) served as the end points. In both age groups, left ventricular tissue samples were collected prior to ischemia (baseline) and after I/R, in non-RIPC controls and in RIPC groups to detect selected pro-survival proteins (Western blot). Maturation did not affect post-ischemic recovery of heart function (Left Ventricular Developed Pressure, LVDP), however, it increased IS and arrhythmogenesis accompanied by decreased levels and activity of several pro-survival proteins and by higher levels of pro-apoptotic proteins in the hearts of elder animals. RIPC reduced the occurrence of reperfusion-induced ventricular arrhythmias, IS and contractile dysfunction in younger animals, and this was preserved in the mature adults. RIPC did not increase phosphorylated protein kinase B (p-Akt)/total Akt ratio, endothelial nitric oxide synthase (eNOS) and protein kinase Cε (PKCε) prior to ischemia but only after I/R, while phosphorylated glycogen synthase kinase-3β (GSK3β) was increased (inactivated) before and after ischemia in both age groups coupled with decreased levels of pro-apoptotic markers. We assume that resistance of rat heart to I/R injury starts to already decline during maturation, and that RIPC may represent a clinically relevant cardioprotective intervention in the elder population.

The timing of propofol administration affects the effectiveness of remote ischemic preconditioning induced cardioprotection in rats

The cardioprotection of remote ischemic preconditioning (RIPC) is abolished under propofol maintained anesthesia. Transient receptor potential vanilloid 1 (TRPV1) channel is present in the heart, and its activation could induce cardioprotection. Therefore, we tested whether the anesthetic propofol administration phase interfered with the RIPC-induced cardioprotection, and RIPC-induced cardioprotection via the cardiac TRPV1 channel. Male Sprague-Dawley rats were subjected to myocardial 30 minutes of ischemia followed by 2 hours of reperfusion. RIPC consisted of three cycles of 5-minute ischemia/reperfusion applied to a hindlimb. Propofol infusion at 12 mg/kg/h was commenced either at 10 minutes before the start of RIPC in the P-pre + RIPC group, or immediately after myocardial ischemia at the onset of reperfusion (P-post + RIPC) while performing RIPC. These two propofol infusion regimes were applied to another two grou bs without RIPC (P-pre and P-post groups). Infarct size (IS) was assessed by triphenyltetrazolium staining. Heart TRPV1 expression was detected by Western blot and immunofluorescence. RIPC significantly reduced myocardial IS compared with the control group (36.7 ± 3% versus 57.2 ± 4%; P < .01). When propofol was started before RIPC, the IS sparing effect of RIPC was completely abolished. However, propofol infusion starting immediately after myocardial ischemia did not affect RIPC-induced cardioprotection. TRPV1 expression significant increase after RIPC, then propofol inhibited the TRPV1 activation of RIPC if given before RIPC but not after. Our results suggest that the timing of propofol administration is critical to preserve the cardioprotection of RIPC. Propofol might cancel RIPC-induced cardioprotection via the cardiac TRPV1 receptor.

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.

Physiological and Pathological Role of TRPV1, TRPV2 and TRPV4 Channels in Heart

Transient receptor potential vanilloid channel 2 (TRPV2) is required for normal cardiac contractility. The stimulation of TRPV1 in isolated cardiomyocytes can aggravate the effect of hypoxia/ reoxygenation (H/R) on H9C2 cells. The knockout of the TRPV1 gene promotes increased tolerance of the isolated perfused heart to the impact of ischemia/reperfusion (I/R). However, activation of TRPV1 increases the resistance of the heart to I/R due to calcitonin gene-related peptide (CGRP) release from afferent nerve endings. It has been established that TRPV1 and TRPV2 are involved in the pathogenesis of myocardial infarction and, in all likelihood, ensure the cardiac tolerance to the ischemia/reperfusion. It has also been documented that the activation of TRPV4 negatively affects the stability of cardiomyocytes to the H/R. The blockade of TRPV4 can be considered as a new approach to the prevention of I/R injury of the heart. Studies also indicate that TRPV1 is involved in the pathogenesis of cardiac hypertrophy and that TRPV2 channels participate in the pathogenesis of dilated cardiomyopathy. Excessive expression of TRPV2 leads to chronic Ca2+- overload of cardiomyocytes, which may contribute to the development of cardiomyopathy.

Involvement of Endothelin 1 in Remote Preconditioning-Induced Cardioprotection through connexin 43 and Akt/GSK-3β Signaling Pathway

The present study was aimed to explore the role of endothelins in remote preconditioning (RP)-induced myocardial protection in ischemia-reperfusion (IR) injury. RP stimulus was given by subjecting hind limb to four cycles of ischemia and reperfuion (5 minutes each) using blood pressure cuff in male rats. Following RP, hearts were isolated and subjected to 30 minutes of ischemia and 120 minutes of reperfusion on Langendorff apparatus. The extent of myocardial injury was determined by measuring the levels of LDH-1, CK-MB and cardiac troponin T (cTnT) in coronary effluent; caspase-3 activity and Bcl 2 expression in heart (apoptosis); infarct size by triphenyl tetrazolium chloride and contractility parameters including left ventricular developed pressure, dp/dt_max dp/dt_min and heart rate. RP reduced ischemia reperfusion-induced myocardial injury, increased the levels of endothelin 1 (in blood), Akt-P, GSK-3β-P and P-connexin 43 (in hearts). Pretreatment with ET_A receptor antagonist, BQ 123 (1 and 2 mg/kg), ET_B receptor antagonist, BQ 788 (1 and 3 mg/kg) and dual inhibitor of ET_A and ET_B receptor, bonsentan (25 and 50 mg/kg) abolished these effects of RP. However, the effects of bonsentan were more pronounced in comparison to BQ 123 and BQ 788. It is concluded that RP stimulus may release endothelin 1 in the blood, which may activate myocardial ET_A and ET_B receptors to trigger cardioprotection through connexin 43 and Akt/GSK-3β pathway.

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.