Increased kallikrein expression protects against cardiac ischemia

Kallikrein/K1, Kinins, and ACE/Kininase II in Homeostasis and in Disease Insight From Human and Experimental Genetic Studies, Therapeutic Implication

Kallikrein-K1 is the main kinin-forming enzyme in organs in resting condition and in several pathological situations whereas angiotensin I-converting enzyme/kininase II (ACE) is the main kinin-inactivating enzyme in the circulation. Both ACE and K1 activity levels are genetic traits in man. Recent research based mainly on human genetic studies and study of genetically modified mice has documented the physiological role of K1 in the circulation, and also refined understanding of the role of ACE. Kallikrein-K1 is synthesized in arteries and involved in flow-induced vasodilatation. Endothelial ACE synthesis displays strong vessel and organ specificity modulating bioavailability of angiotensins and kinins locally. In pathological situations resulting from hemodynamic, ischemic, or metabolic insult to the cardiovascular system and the kidney K1 and kinins exert critical end-organ protective action and K1 deficiency results in severe worsening of the conditions, at least in the mouse. On the opposite, genetically high ACE level is associated with increased risk of developing ischemic and diabetic cardiac or renal diseases and worsened prognosis of these diseases. The association has been well-documented clinically while causality was established by ACE gene titration in mice. Studies suggest that reduced bioavailability of kinins is prominently involved in the detrimental effect of K1 deficiency or high ACE activity in diseases. Kinins are involved in the therapeutic effect of both ACE inhibitors and angiotensin II AT1 receptor blockers. Based on these findings, a new therapeutic hypothesis focused on selective pharmacological activation of kinin receptors has been launched. Proof of concept was obtained by using prototypic agonists in experimental ischemic and diabetic diseases in mice.

Kallikrein(K1)-kinin-kininase (ACE) and end-organ damage in ischemia and diabetes: therapeutic implications

Genetic and pharmacological studies, clinical and experimental, focused on kallikrein-K1, kinin receptors and ACE/kininase II suggest that kinin release in the settings of ischemia or diabetes reduces organ damage, especially in the heart and kidney. Kinin bioavailability may be a limiting factor for efficacy of current kinin-potentiating drugs, like ACE inhibitors. Primary activation of kinin receptors by prototypic pharmacological agonists, peptidase-resistant, selective B1 or B2, displays therapeutic efficacy in experimental cardiac and peripheral ischemic and diabetic diseases. B1R agonism was especially efficient in diabetic animals and had no unwanted effects. Clinical development of kinin receptor agonists may be warranted.

Improvement of endothelial dysfunction in experimental heart failure by chronic RAAS-blockade: ACE-inhibition or AT1-receptor blockade?

Chronic heart failure (CHF) is associated with endothelial dysfunction. Activation of the renin-angiotensin-aldosterone system (RAAS) is believed to be important in the deterioration of endothelial dysfunction in CHF through stimulation of oxidative stress. Whereas angiotensin-converting enzyme inhibitors (ACE-I) improve endothelial function in CHF, the effects of angiotensin II AT1-receptor blockers (ARB) are less well established. Therefore we compared the effects of the ACE-I lisinopril vs. the ARB candesartan on endothelial dysfunction in a rat model of CHF.

CHF was induced by myocardial infarction (MI) after coronary ligation. Two weeks after MI, daily treatment with lisinopril (2 mg/kg) or candesartan cilexetil (1.5 mg/kg) was started. After 13 weeks, rats were sacrificed and endothelial function was determined by measuring acetylcholine (ACh)-induced vasodilation in aortic rings, with selective presence of the nitric oxide synthase (NOS)-inhibitor NG-monomethyl-L-arginine (L-NMMA) to determine the contribution of nitric oxide (NO).

ACh-induced vasodilation was attenuated in untreated MI (-50%) compared with control rats. This was in part due to an impaired contribution of NO (-49%). Lisinopril and candesartan cilexetil fully normalised ACh-induced dilation, including the part mediated by NO.

Chronic RAAS-blockade with lisinopril and candesartan cilexetil normalised endothelial function in CHF in a comparable way. The effect of both treatments included the increase of the NO-mediated dilation, further indicating the important role of oxidative stress in the relationship between the RAAS and endothelial dysfunction in CHF.

Tissue kallikrein is required for the cardioprotective effect of cyclosporin A in myocardial ischemia in the mouse

Clinical and experimental studies suggest that pharmacological postconditioning with Cyclosporin A (CsA) reduces infarct size in cardiac ischemia and reperfusion. CsA interacts with Cyclophilin D (CypD) preventing opening of the mitochondrial permeability transition pore (mPTP). Tissue kallikrein (TK) and its products kinins are involved in cardioprotection in ischemia. CypD knockout mice are resistant to the cardioprotective effects of both CsA and kinins suggesting common mechanisms of action. Using TK gene knockout mice, we investigated whether the kallikrein-kinin system is involved in the cardioprotective effect of CsA. Homozygote and heterozygote TK deficient mice (TK(-/-), TK(+/-)) and wild type littermates (TK(+/+)) were subjected to cardiac ischemia-reperfusion with and without CsA postconditioning. CsA reduced infarct size in TK(+/+) mice but had no effect in TK(+/-) and TK(-/-) mice. Cardiac mitochondria isolated from TK(-/-) mice had indistinguishable basal oxidative phosphorylation and calcium retention capacity compared to TK(+/+) mice but were resistant to CsA inhibition of mPTP opening. TK activity was documented in mouse heart and rat cardiomyoblasts mitochondria. By proximity ligation assay TK was found in close proximity to the mitochondrial membrane proteins VDAC and Tom22, and CypD. Thus, partial or total deficiency in TK induces resistance to the infarct size reducing effect of CsA in cardiac ischemia in mice, suggesting that TK level is a critical factor for cardioprotection by CsA. TK is required for the mitochondrial action of CsA and may interact with CypD. Genetic variability in TK activity has been documented in man and may influence the cardioprotective effect of CsA.

Cardioprotective effects of a selective B(2) receptor agonist of bradykinin post-acute myocardial infarct

BACKGROUND

The cardioprotective benefits of bradykinin are attributable to activation of its B(2) receptor (B(2)R)-mediated actions and abolished by B(2)R antagonists. The current experiments evaluated the cardioprotective potential of a potent, long-acting B(2)R-selective agonist peptide analogue of bradykinin, the compound NG291.

METHODS

We compared the extent of cardiac tissue damage and remodeling and expression pattern of selected genes in mice submitted to acute myocardial infarct (MI) and treated for 1 week with either NG291 [Hyp(3),Thi(5),(N)Chg(7),Thi(8)]-bradykinin or with saline delivered via osmotic minipump.

RESULTS

Active treatment resulted in better ejection fraction (EF) 69 +/- 1% vs. 61 +/- 3.1% (P = 0.01), (vs. 85 +/- 1.3% in sham-operated controls), fractional shortening (FS) 38 +/- 4% vs. 32 +/- 8% (NS) (vs. 53 +/- 1.2 in sham-operated controls), and fewer markers of myocyte apoptosis (TUNEL-positive nuclei 4.9 +/- 1.1% vs. 9.7 +/- 0.03%, P = 0.03). Systolic blood pressure (SBP) at end point was normal at 110 +/- 4.2 in actively treated mice, but tended to be lower at 104 +/- 4.7 mm Hg in saline controls with decreased cardiac systolic capacity. Expression patterns of selected genes to factors related to tissue injury, inflammation, and metabolism (i.e., the B(1)R, B(2)R, endothelial nitric oxide synthase (eNOS), TNF-alpha, cardiomyopathy-associated 3 (Cmya3), and pyruvate dehydrogenase kinase isoenzyme 4 (PDK4)) showed that acute MI induced significant upregulation of these genes, and active treatment prevented or attenuated this upregulation, whereas the B(2)R agonist itself produced no difference in the myocardium of sham-operated mice.

CONCLUSIONS

Treatment with a selective B(2)R agonist initiated at the time of induction of acute MI in mice had a beneficial effect on cardiac function, tissue remodeling, and inflammation-related tissue gene expression, which may explain its structural and functional benefits.

A Novel Category of Anti-Hypertensive Drugs for Treating Salt-Sensitive Hypertension on the Basis of a New Development Concept

Terrestrial animals must conserve water and NaCl to survive dry environments. The kidney reabsorbs 95% of the sodium filtered from the glomeruli before sodium reaches the distal connecting tubules. Excess sodium intake requires the renal kallikrein-kinin system for additional excretion. Renal kallikrein is secreted from the distal connecting tubule cells of the kidney, and its substrates, low molecular kininogen, from the principal cells of the cortical collecting ducts (CD). Formed kinins inhibit reabsorption of NaCl through bradykinin (BK)-B₂ receptors, localized along the CD. Degradation pathway of BK by kinin-destroying enzymes in urine differs completely from that in plasma, so that ACE inhibitors are ineffective. Urinary BK is destroyed mainly by a carboxypeptidase-Y-like exopeptidase (CPY) and partly by a neutral endopeptidase (NEP). Inhibitors of CPY and NEP, ebelactone B and poststatin, respectively, were found. Renal kallikrein secretion is accelerated by potassium and ATP-sensitive potassium (KATP) channel blockers, such as PNU-37883A. Ebelactone B prevents DOCA-salt hypertension in rats. Only high salt intake causes hypertension in animals deficient in BK-B2 receptors, tissue kallikrein, or kininogen. Hypertensive patients, and spontaneously hypertensive rats, excrete less kallikrein than normal subjects, irrespective of races, and become salt-sensitive. Ebelactone B, poststatin, and KATP channel blockers could become novel antihypertensive drugs by increase in urinary kinin levels. Roles of kinin in cardiovascular diseases were discussed.

The Tissue Kallikrein Family of Serine Proteases: Functional Roles in Human Disease and Potential as Clinical Biomarkers

Prostate specific antigen (PSA) or human kallikrein 3 (hK3) has long been an effective biomarker for prostate cancer. Now, other members of the tissue kallikrein (KLK) gene family are fast becoming of clinical interest due to their potential as prognostic biomarkers. particularly for hormone dependent cancers. The tissue kallikreins are serine proteases that are encoded by highly conserved multi-gene family clusters in rodents and humans. The rat and mouse loci contain 10 and 25 functional genes, respectively, while the human locus at 19q 13.4 contains 15 genes. The structural organization and size of these genes are similar across species; all genes have 5 coding exons that encode a prepro-enzyme. Although the physiological activators of these zymogens have not been described, in vitro biochemical studies show that some kallikreins can auto-activate and others can activate each other, suggesting that the kallikreins may participate in an enzymatic cascade similar to that of the coagulation cascade. These genes are expressed, to varying degrees, in a wide range of tissues suggesting a functional involvement in a diverse range of physiological and pathophysiological processes. These include roles in normal skin desquamation and psoriatic lesions, tooth development, neural plasticity, and Alzheimer's disease (AD). Of particular interest is the expression of many kallikreins in prostate, ovarian, and breast cancers where they are emerging as useful prognostic indicators of disease progression.

Attenuation of left ventricular dysfunction by an ACE inhibitor after myocardial infarction in a kininogen-deficient rat model

Bradykinin (BK) coronary outflow and left ventricular (LV) performance of kininogen-deficient Brown Norway Katholiek (BNK) rats and Brown Norway Hannover (BNH) controls were investigated. We analyzed whether the angiotensin-converting enzyme (ACE) inhibitor ramipril is able to attenuate LV dysfunction after induction of myocardial infarction (MI) in this animal model. Ex vivo, the basal BK content in the coronary outflow of buffer-perfused, isolated hearts was measured by specific radioimmunoassay. In vivo, left ventricular pressure (LVP), the maximal rate of LVP increase, LV end-diastolic pressure, the maximal rate of LVP decrease and heart rate were determined using a tip catheter 3 weeks after induction of MI. Compared to BNK rats, basal BK outflow was increased 30-fold in controls (p<0.01). In vivo, we found no significant differences between sham-ligated BNK and BNH rats in basal LV function. After MI, the impairment of LV function was significantly worse in BNK rats when compared to BNH rats. ACE inhibition significantly attenuated this LV dysfunction in both groups, when compared to untreated animals. Reduced basal BK level resulting from kininogen deficiency has no effect on basal LV function, but remains to be a risk factor for the ischemic heart. However, ACE inhibition is sufficient to improve LV function despite kininogen deficiency.

Tissue kallikrein deficiency aggravates cardiac remodelling and decreases survival after myocardial infarction in mice

BACKGROUND

Tissue kallikrein (TK) is a major kinin-releasing enzyme present in arteries. TK is involved in cardioprotection in the setting of acute myocardial ischaemia but its role in post-ischaemic heart failure (HF), a major cause of delayed mortality after myocardial infarction (MI), is unknown.

AIM

To determine whether TK deficiency in the mouse influences survival and cardiac remodelling after MI.

METHODS

MI was induced in 10 week-old male TK-deficient mice and wild-type littermates. Survival was assessed up to 14 months. Cardiac morphological and functional parameters were serially measured by echocardiography. In another experiment, myocardial capillary density and NOS content were evaluated at 3 months.

RESULTS

Infarct size was similar in both genotypes. MI resulted in severe cardiac dysfunction. Up to 12 months after MI, TK(-/-) mice displayed an increased mortality rate (P<0.05, relative risk of death=3.41) and aggravation of left ventricular hypertrophy and dilatation by comparison with TK(+/+) (+18% and +27% respectively, both P<0.05). NOS1 and NOS3 were abnormally regulated in the heart of TK(-/-) mice after MI.

CONCLUSIONS

TK exerts a protective role in HF in mice. Coronary effects are probably involved. As partial genetic deficiency in TK activity occurs in humans, TK-deficient subjects may be at increased risk of mortality in HF.

Genetically altered animals in the study of the metabolic functions of peptide hormone systems

PURPOSE OF REVIEW

Here we review the use of genetically altered animals to address the roles of peptide hormone systems in the modulation of energy homeostasis. Despite the disseminated use of transgenic techniques to establish the functional relevance of several peptide hormone systems, we focus on two multifunctional systems, the renin-angiotensin and the kallikrein-kinin systems. Initially, we explored the background information supporting the functional aspects of these systems, followed by novel knowledge obtained with the phenotypic characterization of genetically altered animals.

RECENT FINDINGS

A role for the renin-angiotensin system in the regulation of adiposity and glucose metabolism has been suggested. Studies using genetically altered animals not only confirmed the physiological relevance of angiotensin II in the control of energy homeostasis, but also revealed that the adipose tissue renin-angiotensin system participates in the endocrine modulation of cardiovascular and renal function. On the other hand, the involvement of the kallikrein-kinin system with metabolic processes was not so obvious. Recent reports using genetically altered animals, however, provided strong evidence to support an important role for kinins in the control of glucose homeostasis and energy balance.

SUMMARY

Here we present examples of how genetically altered animals contribute to a final postulation of the physiological roles of certain hormone systems, bringing new insights into the field.

Neuroprotective role of bradykinin because of the attenuation of pro-inflammatory cytokine release from activated microglia

Bradykinin (BK) has been reported to be a mediator of brain damage in acute insults. Receptors for BK have been identified on microglia, the pathologic sensors of the brain. Here, we report that BK attenuated lipopolysaccharide (LPS)-induced release of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta from microglial cells, thus acting as an anti-inflammatory mediator in the brain. This effect was mimicked by raising intracellular cAMP or stimulating the prostanoid receptors EP2 and EP4, while it was abolished by a cAMP antagonist, a prostanoid receptor antagonist, or by an inhibitor of the inducible cyclooxygenase (cyclooxygenase-2). BK also enhanced formation of prostaglandin E(2) and expression of microsomal prostaglandin E synthase. Expression of BK receptors and EP2/EP4 receptors were also enhanced. Using physiological techniques, we identified functional BK receptors not only in culture, but also in microglia from acute brain slices. BK reduced LPS-induced neuronal death in neuron-microglia co-cultures. This was probably mediated via microglia as it did not affect TNF-alpha-induced neuronal death in pure neuronal cultures. Our data imply that BK has anti-inflammatory and neuroprotective effects in the central nervous system by modulating microglial function.

Mechanisms of Disease: the tissue kallikrein–kinin system in hypertension and vascular remodeling

The pathogenesis of arterial hypertension often involves a rise in systemic vascular resistance (vasoconstriction and vascular remodeling) and impairment of salt excretion in the kidney (inappropriate salt retention despite elevated blood pressure). Experimental and clinical evidence implicate an imbalance between endogenous vasoconstrictor and vasodilator systems in the development and maintenance of hypertension. Kinins (bradykinin and lys-bradykinin) are endogenous vasodilators and natriuretic peptides known best for their ability to antagonize angiotensin-induced vasoconstriction and sodium retention. In humans, angiotensin-converting enzyme inhibitors, a potent class of antihypertensive agents, lower blood pressure at least partially by favoring enhanced kinin accumulation in plasma and target tissues. The beneficial actions of kinins in renal and cardiovascular disease are largely mediated by nitric oxide and prostaglandins, and extend beyond their recognized role in lowering blood pressure to include cardioprotection and nephroprotection. This article is a review of exciting, recently generated genetic, biochemical and clinical data from studies that have examined the importance of the tissue kallikrein-kinin system in protection from hypertension, vascular remodeling and renal fibrosis. Development of novel therapeutic approaches to bolster kinin activity in the vascular wall and in specific compartments in the kidney might be a highly effective strategy for the treatment of hypertension and its complications, including cardiac hypertrophy and renal failure.

Cardiac function and remodeling is attenuated in transgenic rats expressing the human kallikrein-1 gene after myocardial infarction

Bradykinin coronary outflow, left ventricular performance and left ventricular dimensions of transgenic rats harboring the human tissue kallikrein-1 gene TGR(hKLK1) were investigated under basal and ischemic conditions. Bradykinin content in the coronary outflow of buffer-perfused, isolated hearts of controls and TGR(hKLK1) was measured by specific radioimmunoassay before and after global ischemia. Left ventricular function and left ventricular dimensions were determined in vivo using a tip catheter and echocardiography 6 days and 3 weeks after induction of myocardial infarction. Left ventricular type I collagen mRNA expression was analyzed by RNase protection assay. Compared to controls, basal bradykinin outflow was 3.5 fold increased in TGR(hKLK1). Ischemia induced an increase of bradykinin coronary outflow in controls but did not induce a further increase in TGR(hKLK1). However, despite similar unchanged infarction sizes, left ventricular function and remodeling improved in TGR(hKLK1) after myocardial infarction, indicated by an increase in left ventricular pressure (+34%; P<0.05), contractility (dp/dt max. +25%; P<0.05), and in ejection fraction (+20%; P<0.05) as well as by a reduction in left ventricular enddiastolic pressure (-49%, P<0.05), left ventricular enddiastolic diameter (-20%, P<0.05), and collagen mRNA expression (-15%, P<0.05) compared to controls. A chronically activated transgenic kallikrein kinin system with expression of human kallikrein-1 gene counteracts the progression of left ventricular contractile dysfunction after experimental myocardial infarction. Further studies have to show whether these results can be caused by other therapeutically options. Long acting bradykinin receptor agonists might be an alternative option to improve ischemic heart disease.

Genetically altered animal models in the kallikrein-kinin system

Transgenic and gene-targeting technologies allowing the generation of genetically altered animal models have greatly advanced our understanding of the function of specific genes. This is also true for the kallikrein-kinin system (KKS), in which some, but not yet all, components have been functionally characterized using such techniques. The first genetically altered animal model for a KKS component was supplied by nature, the brown Norway rat carrying an inactivating mutation in the kininogen gene. Mice deficient in tissue kallikrein, B1 and B2 receptors, some kinin-degrading enzymes, and factor XII followed, together with transgenic rat and mouse strains overexpressing tissue kallikrein, B1 and B2 receptors, and degrading enzymes. There are still no animal models with genetic alterations in plasma kallikrein, kininases I and some other degrading enzymes. The models have confirmed an important role of the KKS in cardiovascular pathology, inflammation, and pain, and have partially elucidated the distinct function of the two receptors. This created the basis for rational decisions concerning the putative use of kinin receptor agonists and antagonists in therapeutic applications. However, a more thorough analysis of the existing models and the generation of new, more sophisticated transgenic models will be necessary to clarify the still elusive issue as to where and by which mechanisms the kinins exert their actions.

Erythropoietin improves left ventricular function and coronary flow in an experimental model of ischemia-reperfusion injury

BACKGROUND

Recent studies show that erythropoietin (EPO) plays a protective role in brain ischemia. In this condition, administration of EPO protects neurons from ischemic damage. Recently, it has been shown that in patients with chronic heart failure (CHF), EPO treatment improved cardiac function. In the present study we assessed the role of EPO and EPO-receptor (EPO-R) in the heart.

METHODS AND RESULTS

We studied the presence and functionality of the EPO-R in isolated rat hearts in the Langendorff set-up. Hearts were perfused for 20 min with 10 U/ml EPO or vehicle. Immunohistochemistry revealed the presence of the EPO-R on endothelial cells, fibroblasts and to a lesser extent cardiomyocytes. Furthermore, perfusion with EPO resulted in a 50% increase in the phosphorylated MAP kinases p42/p44. To evaluate the protective role of EPO in cardiac ischemia, we performed low-flow (0.6 ml/min) ischemia/reperfusion experiments in isolated rat hearts. Administration of EPO (10 U/ml) reduced the cellular damage by 56% (P<0.05) during reperfusion, diminished apoptosis by 15% (P<0.05) and resulted in a significantly improved recovery of left ventricular pressure (P=0.02) and coronary flow (P=0.01).

CONCLUSION

The present data suggest that a functional EPO-R is present in rat adult cardiac tissue and that exogenous EPO administration improves cardiac function after ischemia/reperfusion injury.

Transgenic activation of the kallikrein-kinin system inhibits intramyocardial inflammation, endothelial dysfunction and oxidative stress in experimental diabetic cardiomyopathy

The mechanisms contributing to diabetic cardiomyopathy, as well as the protective pathways of the kallikrein-kinin-system (KKS), are incompletely understood. In a kallikrein-overexpressing rat model of streptozotocin (STZ)-induced diabetic cardiomyopathy, we investigated the involvement of inflammatory pathways, endothelial dysfunction, and oxidative stress. Six weeks after STZ injection, impairment of left ventricular (LV) function parameters measured by a Millar-tip catheter (peak LV systolic pressure; dP/dtmax; dP/dtmin) was accompanied by a significant increment of ICAM-1 and VCAM-1 (CAMs) expression, as well as of beta2-leukocyte-integrins+ (CD18+, CD11a+, CD11b+) and cytokine (TNF-alpha and IL-1beta)-expressing infiltrates in male Sprague-Dawley (SD-STZ) rats compared with normoglycemic littermates. Furthermore, SD-STZ rats demonstrated a significant impairment of endothelium-dependent relaxation evoked by acetylcholine and significantly increased plasma TBARS (plasma thiobarbituric acid reactive substances) levels as a measure of oxidative stress. These diabetic cardiomyopathy-associated alterations were significantly attenuated (P<0.05) in diabetic transgenic rats expressing the human kallikrein 1 (hKLK1) gene with STZ-induced diabetes. CAMs expression, beta2-leukocyte-integrins+, and cytokine-expressing infiltrates correlated significantly with all evaluated LV function parameters. The multiple protective effects of the KKS in experimental diabetic cardiomyopathy comprise the inhibition of intramyocardial inflammation (CAMs expression, beta2-leukocyte-integrins+ infiltration and cytokine expression), an improvement of endothelium-dependent relaxation and the attenuation of oxidative stress. These insights might have therapeutic implications also for human diabetic cardiomyopathy.

Serine proteases and cardiac function

The serine proteases of the trypsin superfamily are versatile enzymes involved in a variety of biological processes. In the cardiovascular system, the importance of these enzymes in blood coagulation, platelet activation, fibrinolysis, and thrombosis has been well established. Recent studies have shown that trypin-like serine proteases are also important in maintaining cardiac function and contribute to heart-related disease processes. In this review, we describe the biological function of corin, tissue kallikrein, chymase and urokinase and discuss their roles in cardiovascular diseases such as hypertension, cardiac hypertrophy, heart failure, and aneurysm.

Role of tissue kallikrein in the cardioprotective effects of ischemic and pharmacological preconditioning in myocardial ischemia

Tissue kallikrein (TK), a major kinin-forming enzyme, is synthesized in the heart and arteries. We tested the hypothesis that TK plays a protective role in myocardial ischemia by performing ischemia-reperfusion (IR) injury, with and without ischemic preconditioning (IPC) or ACE inhibitor (ramiprilat) pretreatment, in vivo in littermate wild-type (WT) or TK-deficient (TK-/-) mice. IR induced similar infarcts in WT and TK-/-. IPC reduced infarct size by 65% in WT, and by 40% in TK-/- (P<0.05, TK-/- vs WT). Ramiprilat also reduced infarct size by 29% in WT, but in TK-/- its effect was completely suppressed. Pretreatment of WT with a B2, but not a B1, kinin receptor antagonist reproduced the effects of TK deficiency. However, B2 receptor-deficient mice (B2-/-) unexpectedly responded to IPC or ramiprilat like WT mice. But pretreatment of the B2-/- mice with a B1 antagonist suppressed the cardioprotective effects of IPC and ramiprilat. In B2-/-, B1 receptor gene expression was constitutively high. In WT and TK-/- mice, both B2 and B1 mRNA levels increased several fold during IR, and even more during IPC+IR. Thus TK and the B2 receptor play a critical role in the cardioprotection afforded by two experimental maneuvers of potential clinical relevance, IPC and ACE inhibition, during ischemia.

Ischemic preconditioning: emerging evidence, controversy, and translational trials

Protection against ischemia by ischemic preconditioning (IP) is seen in many tissues and organs. However, the preconditioning ischemia must precede lethal ischemia for this effect to occur, and the creation of ischemia to treat heart disease does not seem to be a realistic strategy. Accordingly, the underlying mechanisms that confer cardioprotection should be identified. Early studies revealed that IP causes two windows of cardioprotection, and subsequent efforts to detect cardioprotective factors have identified various triggers, mediators, and potent effectors of IP, such as endogenous receptor agonists (adenosine, catecholamines, bradykinin, and opioids), intracellular messengers [protein kinase C (PKC), p38MAPK, PI-3K, and PKA], ion channels such as KATP channels, enzymes including heat shock proteins (HSPs), superoxide dismutase (SOD), and 5'-nucleotidase, and other factors [nitric oxide (NO), growth factors, free radicals, and products of the arachidonic acid cascade]. Some of these factors are involved in several different pathways and may have multiple roles in IP-induced cardioprotection. Recently, however, certain problems have arisen such as controversies related to increasing knowledge and the relative lack of clinical studies in contrast to the intensive performance of basic studies. To overcome these problems, the latest studies have followed three major trends: (1) investigation of mechanisms to explain the current controversies, (2) detection of other unknown potent mechanisms, and (3) promotion of clinical trials based on the evidence from experimental studies in larger animals. Here, we summarize recent investigations on IP, emphasizing on the controversial issues and emerging factors, and discuss current research on the prevention or treatment of ischemic heart disease including some relevant clinical studies.

Improvement of defective sarcoplasmic reticulum Ca2+transport in diabetic heart of transgenic rats expressing the human kallikrein‐1 gene

The bradykinin-forming enzyme kallikrein-1 is expressed in the heart. To examine whether contractile performance and sarcoplasmic reticulum Ca2+ transport of the diabetic heart can be rescued by targeting the kallikrein-kinin system, we studied left ventricular function and sarcoplasmic reticular Ca2+ uptake after induction of streptozotocin-induced diabetes mellitus in transgenic rats expressing the human tissue kallikrein-1 gene. Six weeks after a single injection of either streptozotocin (70 mg/kg ip) or vehicle, left ventricular performance was determined using a Millar-Tip catheter system. The Ca2+-transporting activity of reticulum-derived membrane vesicles was determined in left ventricular homogenates as oxalate-supported 45Ca2+ uptake. Western blot analysis was used to quantify the reticular Ca2+-ATPase SERCA2a, phospholamban, and the phosphorylation status of the latter. Contractile performance and Ca2+ uptake activity were similar in nondiabetic wild-type and transgenic rats. Severely diabetic wild-type animals exhibited impaired left ventricular performance and decreased reticular Ca2+ uptake (-39% vs. wild-type rats, P<0.05, respectively). These changes were attenuated in diabetic transgenic rats that, in addition, exhibited a markedly increased phospholamban phosphorylation at the Ca2+/calmodulin kinase-specific site threonine17 (2.2-fold vs. diabetic wild-type rats, P<0.05). These transgene-related effects were abolished after treatment with the bradykinin B2 receptor antagonist icatibant (Hoe 140). The SERCA2-to-phospholamban ratio, phosphoserine16-phospholamban levels, and the apparent affinity for Ca2+ of the uptake reaction did not differ between the groups. Increasing the activity of the kallikrein-kinin system by expressing a human kallikrein-1 transgene protects rat heart against diabetes-induced contractile and reticular Ca2+ transport dysfunctions. An increased phosphorylation of the SERCA2 regulatory protein phospholamban at threonine17 via a B2 receptor-mediated mechanism is thereby involved.

Immunohistochemical Distributions of the Tissue Kallikrein-Kinin System in Ischemic and Non-Ischemic Mouse Heart

Kinins have been shown to play a cardioprotective role during myocardial ischemia. However, the localization of each of the components of the kallikrein-kinin system in the heart has not been determined in a cell type-specific manner. Recently, mK1 has been identified as the major tissue kallikrein with the strongest bradykinin-forming activity among the products of the mouse tissue kallikrein gene superfamily. In the study presented here, we investigated the localizations of mK1, kininogen and bradykinin B2 receptors (B2Rs) in ischemic and non-ischemic left ventricles by immunohistochemistry. Kininogen, which contains bradykinin as a surface epitope, was detected by an anti-bradykinin antibody. Changes in the amounts of mK1 and B2R were evaluated by Western blot analysis. Myocardial ischemia was induced by ligation of the left anterior descending coronary artery for 60 min followed by reperfusion for 24 h. mK1 and B2Rs were most abundantly expressed in the vascular endothelium and, to a lesser extent, in fibroblasts. No immunohistochemical signal of these molecules was detected in myocytes. Kininogen was localized in the vascular endothelium and the smooth muscle layer. Myocardial ischemia, although it had no effect on the localization of these molecules, increased the amounts of mK1 and B2R. We have obtained immunohistochemical evidence that all components of the tissue kallikrein-kinin system are present in the mouse heart. The coronary artery is the major site of kallikrein-kinin activity both in ischemic and non-ischemic hearts.

Les récepteurs de la bradykinine : de nouveaux rôles physiopathologiques

In addition to being a pro-inflammatory mediator, bradykinin is now recognized as a neuromediator and regulator of several vascular and renal functions. New breakthroughs point to unusual and atypical signalling pathways for a G-protein coupled receptor that could explain the anti-proliferative and anti-fibrogenic effects of bradykinin. The availability of transgenic and knock out animal models for bradykinin receptors or bradykinin-synthesizing or -catabolic enzymes confirms these cardiac and renal protective roles for this peptide system. Bradykinin receptors are involved in the therapeutic action of angiotensin-1 converting enzyme inhibitors that are used in the treatment of arterial hypertension, heart failure and diabetes. Nevertheless, recent evidence highlights dissimilar mechanisms in the regulation and function of these receptors between the central nervous system and peripheral tissues. Therefore, the development of more specific bradykinin receptor agonists or antagonists devoid of central actions seems to evolve as a new therapeutic approach.

Calcium antagonist clevidipine reduces myocardial reperfusion injury by a mechanism related to bradykinin and nitric oxide

Certain calcium antagonists, in addition to their classic actions, can increase blood flow during ischemia via bradykinin- and nitric oxide (NO)-dependent mechanisms and protect the ischemic myocardium against reperfusion injury by enhancing NO bioavailability. The current study aimed to investigate the possible involvement of bradykinin and NO in the cardioprotective action of the short-acting calcium antagonist clevidipine during late ischemia and reperfusion. Anesthetized pigs were subjected to 45-min ligation of the left anterior descending coronary artery (LAD) followed by 4 h of reperfusion. Four groups were given vehicle, clevidipine, clevidipine in combination with the bradykinin B2 receptor antagonist HOE 140 or clevidipine in combination with HOE 140 and the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP) into the LAD during the last 10 min of ischemia and the first 5 min of reperfusion. There were no significant differences in hemodynamics among the groups before ischemia or during ischemia-reperfusion. The infarct size (IS) was 87% +/- 2% of the area at risk in the vehicle group. Clevidipine reduced the IS to 60% +/- 3% (p < 0.001 vs vehicle). When clevidipine was administered together with HOE 140, the protective effect of clevidipine was abolished (IS, 80% +/- 3%; p < 0.001 vs clevidipine), whereas addition of SNAP restored cardioprotection (IS, 62% +/- 5%; p < 0.001 vs vehicle). The increase in LAD blood flow by endothelium-dependent dilator substance P was significantly larger in the clevidipine group than in the other groups. The results suggest that the cardioprotective effect of clevidipine during late ischemia and early reperfusion is mediated via bradykinin- and NO-related mechanisms.

Detrimental implication of B1 receptors in myocardial ischemia: evidence from pharmacological blockade and gene knockout mice

OBJECTIVE

The aim of this study was to evaluate the contribution of kinin B1 receptors in myocardial ischemia using both pharmacological blockade and gene knockout mice.

MATERIAL AND METHODS

Hearts (n = 6-8 per group) from wild type or homozygous B1 receptor gene knockout mice were isolated and perfused using the Langendorff technique. After a 30-min stabilisation period, the left coronary artery was occluded for 30 min followed by 60 min of reperfusion. In two separate groups of wild type hearts, B1 and B2 receptors were blocked with 3 nM of (des-Arg9, Leu8)-bradykinin and 10 nM of Hoe 140, respectively, (started 15 min before ischemia and stopped before the reperfusion).

RESULTS

Infarct size to risk zone (I/R) ratio was significantly reduced in hearts of knockout mice (11.3 +/- 2.1%) compared to those of wild type mice (25.7 +/- 1.7%). Furthermore, in wild type mice, I/R was significantly reduced in hearts perfused with the B1 receptor antagonist (12.8 +/- 2.4%) but not in hearts perfused with the B2 receptor antagonist (36.3 +/- 4.4%) compared to untreated hearts. Finally, a RT-PCR technique showed an activation of kinin B1 receptor gene transcription, in wild type hearts, subjected to the ischemia-reperfusion sequence.

CONCLUSION

This study demonstrates that B1 receptors are induced during myocardial ischemia where they could play a detrimental role in mice.

Efficacy of angiotensin II type 1 receptor blockade on reperfusion-induced arrhythmias and mortality early after myocardial infarction is increased in transgenic rats with cardiac angiotensin II type 1 overexpression

Angiotensin II induces ischemia/reperfusion (I/R)-induced arrhythmias and blockade of the angiotensin II type 1 receptor (AT1R) may therefore be beneficial in preventing arrhythmias and decreasing mortality after myocardial infarction (MI). Because the AT1R is upregulated after myocardial ischemia, it was hypothesized that the level of AT1R expression would mediate the response to AT1R blockade. Transgenic (TGR) rats that overexpress the human AT1R and Sprague-Dawley rats were used as controls. Total duration of arrhythmia (seconds) after I/R injury was similar in TGR and SD rats (433 +/- 109 vs. 376 +/- 117, p = n.s.). AT1R blockade with losartan decreased total duration of arrhythmia in the TGR rats (433 +/- 110 s-164 +/- 48 s; p < 0.05), whereas it caused a nonsignificant increase in the SD rats (376 +/- 117 s-497 +/- 97). In vivo, survival in the first 24 hours after MI was impaired in TGR rats (39%; SD, 63%). Losartan improved survival significantly in TGR rats (from 39% to 80%, p < 0.05). A smaller, nonsignificant effect was observed in SD rats (63% to 81%). AT1R blockade is beneficial only when the AT1R was overexpressed, both in reducing the reperfusion-induced arrhythmias and mortality early after MI.

Multiple interactions between the renin-angiotensin and the kallikrein-kinin systems: role of ACE inhibition and AT1 receptor blockade

The investigation of therapeutic actions of angiotensin type 1 (AT1) receptor antagonists and ACE inhibitors (ACEI) demonstrated complex interactions between the renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS) in several experimental and clinical studies. They are evidenced by the fact that (1) ACE efficiently catabolizes kinins; (2) angiotensin-derivatives such as ANG-(1-7) exert kininlike effects; and (3) kallikrein probably serves as a prorenin-activating enzyme. (4) Several authors have demonstrated experimentally that the protective effects of ACEI are at least partly mediated by a direct potentiation of kinin receptor response on BK stimulation. (5) Furthermore, studies on AT1 antagonists, which do not directly influence kinin degradation, and studies on angiotensin-receptor transgenic mice have revealed additional interactions between the RAS and the KKS. There is mounting evidence that an autocrine cascade including kinins, nitric oxide, prostaglandins, and cyclic GMP is involved in at least some of the angiotensin type 2 receptor effects. This review discusses multiple possibilities of cross-talks between the RAS and KKS in vascular and cardiac physiology and pathology after ACE inhibition and AT1 receptor blockade.

Molecular interactions of vasoactive systems in cardiovascular damage

The renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS) are important in the aetiology of hypertension and the pathogenesis of cardiac and renal damage associated with elevated blood pressure. While angiotensin II acts by increasing blood pressure and supporting end-organ damage, kinins have an opposite protective effect. The two systems interact on many levels. Angiotensin-converting enzyme (ACE) activates angiotensins and inactivates kinins. ACE inhibitors therefore exert their organ-protective action via both systems, as they block the deleterious RAS and potentiate the protective KKS. Furthermore, ACE may directly interact with the kinin B2 receptor and ACE inhibitors, thereby eliciting a resensitization of this receptor following agonist-induced desensitization. Recently, a functional heterodimer of AT1 and B2 receptors has also been demonstrated. Moreover, kallikreins may be involved in the activation of prorenin and in the signalling pathway of angiotensin AT2 receptors. Because of the multitude of interactions, any therapeutic intervention into one of the two peptide systems will automatically lead to an alteration in the other. This double action is utilized by drugs such as ACE inhibitors to provide unprecedented effectiveness in hypertension and associated cardiac and renal damage.

Targeting kinin receptors for the treatment of tissue ischaemia

Kinins, the biological end-products of the kallikrein-kininogen system, influence many aspects of the cellular function. Interest in this peptidergic system has been renewed recently by the discovery that kinins exert cardiovascular protective effects and promote post-ischaemic recovery by stimulating vascular growth. Pharmacological and genetic studies indicate that induction of kallikrein and kinin receptors by ischaemia is functionally relevant in the natural host response that permits perfusion recovery and tissue healing. Furthermore, potentiation of the generation of kinins by continuous supply of tissue kallikrein promotes reparative angiogenesis through stimulation of the release of nitric oxide and prostaglandins. Strategies that activate kinin receptors might be applicable to the treatment of occlusive vascular disease, whereas kinin receptor antagonists could represent therapeutic reagents against pathological angiogenesis in cancer and chronic inflammatory conditions.