Bradykinin preconditioning in coronary artery bypass grafting

Melatonin as a protective agent in cardiac ischemia-reperfusion injury: Vision/Illusion?

Melatonin, an emphatic endogenous molecule exerts protective effects either via activation of G-protein coupled receptors (Melatonin receptors, MTR 1-3), tumor necrosis factor receptor (TNFR), toll like receptors (TLRS), nuclear receptors (NRS) or by directly scavenging the free radicals. MTRs are extensively expressed in the heart as well as in the coronary vasculature. Accumulating evidences have indicated the existence of a strong correlation between reduction in the circulating level of melatonin and precipitation of heart attack. Apparently, melatonin exhibits cardioprotective effects via modulating inextricably interlinked pathways including modulation of mitochondrial metabolism, mitochondrial permeability transition pore formation, nitric oxide release, autophagy, generation of inflammatory cytokines, regulation of calcium transporters, reactive oxygen species, glycosaminoglycans, collagen accumulation, and regulation of apoptosis. Convincingly, this review shall describe the various signaling pathways involved in salvaging the heart against ischemia-reperfusion injury.

Kallikrein-kinin system as the dominant mechanism to counteract hyperactive renin-angiotensin system

The renin-angiotensin system (RAS) generates, maintains, and makes worse hypertension and cardiovascular diseases (CVDs) through its biologically active component angiotensin II (Ang II), that causes vasoconstriction, sodium retention, and structural alterations of the heart and the arteries. A few endogenous vasodilators, kinins, natriuretic peptides, and possibly angiotensin (1-7), exert opposite actions and may provide useful therapeutic agents. As endothelial autacoids, the kinins are potent vasodilators, active natriuretics, and protectors of the endothelium. Indeed, the kallikrein-kinin system (KKS) is considered the dominant mechanism for counteracting the detrimental effects of the hyperactive RAS. The 2 systems, RAS and KKS, are controlled by the angiotensin-converting enzyme (ACE) that generates Ang II and inactivates the kinins. Inhibitors of ACE can reduce the impact of Ang II and potentiate the kinins, thus contributing to restore the cardiovascular homeostasis. In the last 20 years, ACE-inhibitors (ACE-Is) have become the drugs of first choice for the treatments of the major CVDs. ACE-Is not only reduce blood pressure, as sartans also do, but by protecting and potentiating the kinins, they can reduce morbidity and mortality and improve the quality of life for patients with CVDs. This paper provides a brief review of the literature on this topic.

Extracellular signalling molecules in the ischaemic/reperfused heart - druggable and translatable for cardioprotection?

In patients with acute myocardial infarction, timely reperfusion is essential to limit infarct size. However, reperfusion also adds to myocardial injury. Brief episodes of ischaemia/reperfusion in the myocardium or on organ remote from the heart, before or shortly after sustained myocardial ischaemia effectively reduce infarct size, provided there is eventual reperfusion. Such conditioning phenomena have been established in many experimental studies and also translated to humans. The underlying signal transduction, that is the molecular identity of triggers, mediators and effectors, is not clear yet in detail, but several extracellular signalling molecules, such as adenosine, bradykinin and opioids, have been identified to contribute to cardioprotection by conditioning manoeuvres. Several trials have attempted the translation of cardioprotection by such autacoids into a clinical scenario of myocardial ischaemia and reperfusion. Adenosine and its selective agonists reduced infarct size in a few studies, but this benefit was not translated into improved clinical outcome. All studies with bradykinin or drugs which increase bradykinin's bioavailability reported reduced infarct size and some of them also improved clinical outcome. Synthetic opioid agonists did not result in a robust infarct size reduction, but this failure of translation may relate to the cardioprotective properties of the underlying anaesthesia per se or of the comparator drugs. The translation of findings in healthy, young animals with acute coronary occlusion/reperfusion to patients of older age, with a variety of co-morbidities and co-medications, suffering from different scenarios of myocardial ischaemia/reperfusion remains a challenge.

Adjuvant cardioprotection in cardiac surgery: update

Cardiac surgery patients are now more risky in terms of age, comorbidities, and the need for complex procedures. It brings about reperfusion injury, which leads to dysfunction and/or loss of part of the myocardium. These groups of patients have a higher incidence of postoperative complications and mortality. One way of augmenting intraoperative myocardial protection is the phenomenon of myocardial conditioning, elicited with brief nonlethal episodes of ischaemia-reperfusion. In addition, drugs are being tested that mimic ischaemic conditioning. Such cardioprotective techniques are mainly focused on reperfusion injury, a complex response of the organism to the restoration of coronary blood flow in ischaemic tissue, which can lead to cell death. Extensive research over the last three decades has revealed the basic mechanisms of reperfusion injury and myocardial conditioning, suggesting its therapeutic potential. But despite the enormous efforts that have been expended in preclinical studies, almost all cardioprotective therapies have failed in the third phase of clinical trials. One reason is that evolutionary young cellular mechanisms of protection against oxygen handling are not very robust. Ischaemic conditioning, which is among these, is also limited by this. At present, the prevailing belief is that such options of treatment exist, but their full employment will not occur until subquestions and methodological issues with the transfer into clinical practice have been resolved.

The kallikrein-kinin system as a regulator of cardiovascular and renal function

Autocrine, paracrine, endocrine, and neuroendocrine hormonal systems help regulate cardio-vascular and renal function. Any change in the balance among these systems may result in hypertension and target organ damage, whether the cause is genetic, environmental or a combination of the two. Endocrine and neuroendocrine vasopressor hormones such as the renin-angiotensin system (RAS), aldosterone, and catecholamines are important for regulation of blood pressure and pathogenesis of hypertension and target organ damage. While the role of vasodepressor autacoids such as kinins is not as well defined, there is increasing evidence that they are not only critical to blood pressure and renal function but may also oppose remodeling of the cardiovascular system. Here we will primarily be concerned with kinins, which are oligopeptides containing the aminoacid sequence of bradykinin. They are generated from precursors known as kininogens by enzymes such as tissue (glandular) and plasma kallikrein. Some of the effects of kinins are mediated via autacoids such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and/or tissue plasminogen activator (tPA). Kinins help protect against cardiac ischemia and play an important part in preconditioning as well as the cardiovascular and renal protective effects of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARB). But the role of kinins in the pathogenesis of hypertension remains controversial. A study of Utah families revealed that a dominant kallikrein gene expressed as high urinary kallikrein excretion was associated with a decreased risk of essential hypertension. Moreover, researchers have identified a restriction fragment length polymorphism (RFLP) that distinguishes the kallikrein gene family found in one strain of spontaneously hypertensive rats (SHR) from a homologous gene in normotensive Brown Norway rats, and in recombinant inbred substrains derived from these SHR and Brown Norway rats this RFLP cosegregated with an increase in blood pressure. However, humans, rats and mice with a deficiency in one or more components of the kallikrein-kinin-system (KKS) or chronic KKS blockade do not have hypertension. In the kidney, kinins are essential for proper regulation of papillary blood flow and water and sodium excretion. B2-KO mice appear to be more sensitive to the hypertensinogenic effect of salt. Kinins are involved in the acute antihypertensive effects of ACE inhibitors but not their chronic effects (save for mineralocorticoid-salt-induced hypertension). Kinins appear to play a role in the pathogenesis of inflammatory diseases such as arthritis and skin inflammation; they act on innate immunity as mediators of inflammation by promoting maturation of dendritic cells, which activate the body's adaptive immune system and thereby stimulate mechanisms that promote inflammation. On the other hand, kinins acting via NO contribute to the vascular protective effect of ACE inhibitors during neointima formation. In myocardial infarction produced by ischemia/reperfusion, kinins help reduce infarct size following preconditioning or treatment with ACE inhibitors. In heart failure secondary to infarction, the therapeutic effects of ACE inhibitors are partially mediated by kinins via release of NO, while drugs that activate the angiotensin type 2 receptor act in part via kinins and NO. Thus kinins play an important role in regulation of cardiovascular and renal function as well as many of the beneficial effects of ACE inhibitors and ARBs on target organ damage in hypertension.

Remote ischaemic preconditioning down-regulates kinin receptor expression in neutrophils of patients undergoing heart surgery

OBJECTIVES

Remote ischaemic preconditioning (RIPC) may protect distant organs against ischaemia-reperfusion injury. We investigated the impact of RIPC on kinin receptor expression in neutrophils following RIPC in patients undergoing coronary artery bypass grafting (CABG).

METHODS

Patients undergoing elective CABG with cardiopulmonary bypass (CPB) were randomized to RIPC (n = 15) or control (n = 15) groups. The study group underwent RIPC by inflation of a blood pressure cuff on the arm. Expression of kinin receptors, plasma concentrations of IL-6, IL-8, IL-10, TNF-α and neutrophil elastase were determined at baseline (before RIPC/sham), immediately before surgery (after RIPC/sham) and 30 min and 24 h after surgery. Plasma bradykinin levels were assessed before and after RIPC/sham, and at 30 min, 6, 12 and 24 h after surgery. Serum creatine kinase (CK), troponin I, C-reactive protein (CRP) and lactate levels were measured immediately prior to surgery and 30 min, 6, 12, 24 and 48 h after surgery.

RESULTS

Kinin B2 receptor expression did not differ between the groups at baseline (pre-RIPC), but was significantly lower in the RIPC group than in the control group after RIPC/sham (P < 0.05). Expressions of both kinin B1 and B2 receptors were significantly down-regulated in the RIPC group, and this persisted to 24 h after surgery (P < 0.001). Neutrophil elastase levels were significantly increased after surgery. There were no differences in CK, CRP, cytokine, lactate or troponin I levels between the groups.

CONCLUSIONS

RIPC down-regulated the expression of kinin B1 and B2 receptors in neutrophils of patients undergoing CABG.

Cardioprotection during cardiac surgery

Coronary heart disease (CHD) is the leading cause of morbidity and mortality worldwide. For a large number of patients with CHD, coronary artery bypass graft (CABG) surgery remains the preferred strategy for coronary revascularization. Over the last 10 years, the number of high-risk patients undergoing CABG surgery has increased significantly, resulting in worse clinical outcomes in this patient group. This appears to be related to the ageing population, increased co-morbidities (such as diabetes, obesity, hypertension, stroke), concomitant valve disease, and advances in percutaneous coronary intervention which have resulted in patients with more complex coronary artery disease undergoing surgery. These high-risk patients are more susceptible to peri-operative myocardial injury and infarction (PMI), a major cause of which is acute global ischaemia/reperfusion injury arising from inadequate myocardial protection during CABG surgery. Therefore, novel therapeutic strategies are required to protect the heart in this high-risk patient group. In this article, we review the aetiology of PMI during CABG surgery, its diagnosis and clinical significance, and the endogenous and pharmacological therapeutic strategies available for preventing it. By improving cardioprotection during CABG surgery, we may be able to reduce PMI, preserve left ventricular systolic function, and reduce morbidity and mortality in these high-risk patients with CHD.

Myocardial postconditioning: next step to cardioprotection

Myocardial ischemia is a condition in which lack of blood flow to the cardiac muscle occurs resulting in deficient oxygen and nutrient supply to the heart. The restoration of blood flow to an organ or tissue is termed reperfusion. Brief episodes of ischemia and reperfusion given after prolonged ischemia and at the onset of reperfusion denotes postconditioning. Myocardial postconditioning is a phenomenon in which myocardium from lethal ischemia-reperfusion injury is protected. However, numerous experimental studies reveal that the cardioprotective effects of postconditioning are suppressed in various pathological states. This review critically discusses the mechanisms involved in the cardioprotective effects of postconditioning and factors affecting the cardioprotective potential of myocardial postconditioning.

Kallikrein-kinin system: a surgical perspective in post-aprotinin era

Kallikrein-kinin system (KKS) plays an important role in inflammation, ischemia-reperfusion (IR) injury, and development of neoplasia. There is evidence to suggest that KKS plays an important role in organ protection during preconditioning. Aprotinin is a nonspecific serine protease inhibitor, which has been extensively used in cardiac surgery for the control of post operative bleeding. The anti-inflammatory effects of aproprotin are due to its inhibitory effect on the kallikrein-kinin system (KKS). We herein review KKS and its role as applied to the practice of surgery.

Remote ischemic preconditioning stimulus decreases the expression of kinin receptors in human neutrophils

BACKGROUND

Remote ischemic preconditioning (RIPC) has been shown to reduce ischemic-reperfusion injury and is induced by brief forearm ischemia. Kinins are known to be involved in RIPC and act via the G protein coupled B1 and B2 receptors. Interaction of the kinins with their respective receptors causes receptor internalization, thereby reducing the potential for further activation. This may be critical for the protective effect of RIPC and if so, we hypothesized, would significantly decrease the expression of kinin receptors on the surface of neutrophils.

METHODS

The study was performed on five healthy human volunteers. The left forearm was rendered ischemic for three 5-min periods, each separated by 5 min of reperfusion. Three venous blood samples were taken from the right arm, one before and two after RIPC. Neutrophil isolation, immunofluorescence labeling, and confocal microscopy were performed. Mean pixel intensity data were generated using a fixed circular area of interest (AOI, 40×40 μm). For every image, the AOI was placed over a cell and the mean pixel intensity was recorded. The mean intensity was expressed as pixel×10(2)/μm(2) and presented as mean±SEM. Immunofluorescence at the different time points was compared by one way analysis of variance with Bonferroni's post-hoc test. A P value<0.05 was considered significant.

RESULTS

The mean pixel intensity for kinin B1 receptors was decreased at 24 h after RIPC compared with both baseline and 15 min after RIPC (P<0.001). Similarly, the intensity for B2 receptor labeling on neutrophils was significantly decreased 24 h after RIPC compared with the baseline value (P<0.001).

CONCLUSIONS

RIPC decreases expression of kinin receptors on circulating human neutrophils. Reduction in kinin surface receptors suggests internalization of receptors and is consistent with the concepts of kinin receptor activation and their role in RIPC.

Bradykinin protects against brain microvascular endothelial cell death induced by pathophysiological stimuli

The morphological and functional integrity of the microcirculation is compromised in many cardiovascular diseases such as hypertension, diabetes, stroke, and sepsis. Angiotensin converting enzyme inhibitors (ACEi), which are known to favor bradykinin (BK) bioactivity by reducing its metabolism, may have a positive impact on preventing the microvascular structural rarefaction that occurs in these diseases. Our study was designed to test the hypothesis that BK, via B2 receptors (B2R), protects the viability of the microvascular endothelium exposed to the necrotic and apoptotic cell death inducers H(2)O(2) and LPS independently of hemodynamics. Expression (RT-PCR and radioligand binding) and functional (calcium mobilization with fura-2AM, and p42/p44MAPK and Akt phosphorylation assays) experiments revealed the presence of functional B2R in pig cerebral microvascular endothelial cells (pCMVEC). In vitro results showed that the cytocidal effects of H(2)O(2) and LPS on pCMVEC were significantly decreased by a BK pretreatment (MTT and crystal violet tests, annexin-V staining/FACS analysis), which was countered by the B2R antagonist HOE 140. BK treatment coincided with enhanced expression of the cytoprotective proteins COX-2, Bcl-2, and (Cu/Zn)SOD. Ex vivo assays on rat brain explants showed that BK impeded (by approximately 40%) H(2)O(2)-induced microvascular degeneration (lectin-FITC staining). The present study proposes a novel role for BK in microvascular endothelial protection, which may be pertinent to the complex mechanism of action of ACEi explaining their long-term beneficial effects in maintaining vascular integrity.

'Conditioning' the heart during surgery

Coronary heart disease (CHD) is the leading cause of death worldwide. Coronary artery bypass graft (CABG) surgery remains the procedure of choice for coronary artery revascularisation in a large number of patients with severe CHD. However, the profile of patients undergoing CABG surgery is changing with increasingly higher-risk patients being operated upon, resulting in significant morbidity and mortality in this patient group. Myocardial injury sustained during cardiac surgery, most of which can be attributed to acute myocardial ischaemia-reperfusion injury, is associated with worse short-term and long-term clinical outcomes. Clearly, new treatment strategies are required to protect the heart during cardiac surgery in terms of reducing myocardial injury and preserving left ventricular systolic function, such that clinical outcomes can be improved. 'Conditioning' the heart to harness its endogenous cardioprotective capabilities using either brief ischaemia or pharmacological agents, provides a potentially novel approach to myocardial protection during cardiac surgery, and is the subject of this review article.

Bradykinin induces microvascular preconditioning through the opening of calcium-activated potassium channels

BACKGROUND

This study was designed to investigate whether the activation of calcium-activated potassium (K(Ca)) or adenosine triphosphate sensitive potassium (K(ATP)) channels are required for bradykinin-induced microvascular preconditioning.

METHODS

Isolated rabbit hearts underwent retrograde perfusion with Krebs-Henseleit buffer (KHB) followed by 60 minutes of ischemic arrest with cold crystalloid cardioplegia (CCCP). Eight CCCP hearts received no pretreatment. Six bradykinin-preconditioned hearts received a 10-minute coronary infusion of 10(-8) mol/L bradykinin-enriched KHB followed by a 5-minute recovery period before CCCP. Six hearts received both 10(-8) mol/L charybdotoxin (a K(Ca) channel blocker) and bradykinin preconditioning. Finally, 6 other hearts received 10(-5 degrees ) mol/L glibenclamide (a K(ATP) channel blocker) to bradykinin-enriched KHB. All hearts were reperfused for 30 minutes with KHB.

RESULTS

Bradykinin preconditioning significantly improved the recovery of left ventricular and microvascular function, as compared with control. On the other hand, bradykinin preconditioning significantly reduced the contractile responses to U46619, a thromboxane A2 analogue. Charybdotoxin significantly inhibited the improved recovery of bradykinin-induced left ventricular and microvascular function. Glibenclamide tended to diminish the bradykinin preconditioning-enhanced recovery of left ventricular function, but failed to affect bradykinin preconditioning-improved recovery of microvascular function.

CONCLUSION

Both K(Ca) and K(ATP) channels were involved partially in bradykinin-induced myocardial preconditioning. However, bradykinin induces microvascular preconditioning through the opening of K(Ca) channels rather than K(ATP) channels.

Bradykinin preconditioning improves the profile of cell survival proteins and limits apoptosis after cardioplegic arrest

BACKGROUND

We hypothesized that preconditioning the heart with bradykinin (BK) would improve the profile of antiapoptotic proteins and inhibit myocardial apoptosis.

METHODS AND RESULTS

Eighteen rabbit hearts were retrogradely perfused with Krebs-Henseleit buffer (KHB). Six control hearts were perfused with KHB for 90 minutes without cardioplegia ischemia. Six hearts were arrested for 30 minutes (37 degrees C) with crystalloid cardioplegia (CCP). Six BK preconditioning (BKPC) hearts received a 10-minute coronary infusion of 10(-8) M BK-enriched KHB followed by a 5-minute recovery period and were then arrested for 30 minutes with CCP. The hearts were reperfused for 30 minutes with KHB. BKPC significantly improved the recovery of left ventricular pressure (73+/-5 versus 51+/-4 mm Hg; P<0.05) and reduced the percentage of myocardial apoptosis (3.4+/-0.3% versus 1.2+/-0.2%; P<0.05) as compared with CCP. There were no significant differences in total protein levels of caspase 3, Bcl-2, Bad, and Bax, among the groups. Both BKPC and CCP induced phosphorylation of Bad at Ser112, but the BKPC group had higher phosphorylated Bad than CCP (4.4+/-0.5 versus 2.0+/-0.3; P<0.05). Both BKPC and CCP alone increased caspase 3 cleavage and activity as compared with controls (P<0.05 and P<0.01, respectively), but BKPC caused less cleavage and activation of caspase 3 than CCP alone (P<0.05).

CONCLUSIONS

BKPC increased Bad phosphorylation, inhibited caspase 3 activation, and limited myocardial apoptosis, which were associated with improvement of left-ventricular performance. These results identify novel molecular mechanisms underlying the protective effects of BKPC during cardiac surgery.

Bradykinin Preconditioning Preserves Coronary Microvascular Reactivity During Cardioplegia–Reperfusion

BACKGROUND

Alterations of microvascular reactivity reduce myocardial perfusion after ischemic cardioplegia. We hypothesized that bradykinin preconditioning (BKPC) would preserve endothelium-dependent microvascular responses and improve myocardial function after cardioplegic ischemia-reperfusion.

METHODS

Rabbit hearts were perfused with Krebs-Henseleit buffer (KHB). The hearts were arrested for 60 minutes with moderately cold (25 degrees C) crystalloid cardioplegia (MCCP, n = 8) or with cold (0 degrees to 4 degrees C) crystalloid cardioplegia (CCCP) (n = 6). The BKPC hearts received a 10-minute coronary infusion of 10(-8) M BK-enriched KHB, followed by a 5-minute recovery period, and then were arrested for 60 minutes with MCCP (BKPC + MCCP, n = 8) or with CCCP (BKPC + CCCP, n = 6). The hearts were reperfused for 30 minutes with KHB. Six control hearts were perfused with KHB for 90 minutes without cardioplegia-ischemia. Left ventricle performance was measured, and in vitro relaxation responses of precontracted coronary arterioles (internal diameter, 80 to 150 mum) were obtained in a pressurized no-flow state.

RESULTS

Ischemic arrest with MCCP or CCCP markedly reduced endothelium-dependent relaxation to adenosine 5'-diphosphate, substance P, and calcium ionophore (A23187). Both MCCP and CCCP significantly enhanced contractile responses to U46619 (10(-7) M), a thromboxane A2 analogue, compared with control (p < 0.05). In contrast, BKPC significantly improved the recovery of endothelium-dependent relaxation to adenosine 5'-diphosphate, substance P, and A23187 compared with MCCP or CCCP, respectively. BKPC reduced the contractile responses to U46619 compared with MCCP or CCCP. BKPC also improved postischemic performance compared with MCCP or CCCP alone (p < 0.05).

CONCLUSIONS

BKPC preserves endothelium-dependent microvascular responses and prevents the hypercontractility to U46619. These effects may provide increased coronary perfusion and prevent arteriolar spasm after open heart surgery. They suggest that BK preconditions the coronary microvasculature during cardiovascular surgery.

Pharmacological Preconditioning With Bradykinin Affords Myocardial Protection Through NO-dependent Mechanisms

Bradykinin (BK) is one of the triggers of ischemic preconditioning. Protein kinase C (PKC) and mitochondrial ATP-dependent potassium (K(ATP)) channels are central factors in cardioprotection afforded by BK. However, the role of nitric oxide (NO) in the early phase protection of preconditioning with BK is not well understood. We assessed the signaling pathway of the early phase protection of pharmacological preconditioning afforded by BK. Isolated perfused rat hearts (n = 8/group) were subjected to 30-minute global ischemia and 50-minute reperfusion. Left ventricular systolic pressure (LVSP) was recorded prior to the global ischemia and at the end of reperfusion. Preconditioning with BK was induced by two cycles of 5-minute infusion of BK (0.5 micromol/L) and 5-minute washout prior to the global ischemia. To examine participants in the signaling pathway, 5-hydroxydecanoate (5-HD, 200 micromol/L), chelerythrine (CH, 5 micromol/L), or N(omega)-nitro-L-arginine methyl ester (L-NAME, 50 mmol/L) was added to the perfusate for 5 minutes prior to the infusion of BK. Pharmacological preconditioning by BK improved postischemic recovery of LVSP (+ 45.1% versus control, P < 0.01). Protection by BK was abolished by coadministration of CH, 5-HD, or L-NAME. BK affords myocardial protection in the early phase of pharmacological preconditioning through a pathway that includes endogenous NO, PKC, and mitochondrial K(ATP) channels.