Tissue Kallikrein Is Involved in the Cardioprotective Effect of AT1-Receptor Blockade in Acute Myocardial Ischemia

Inflammatory Bowel Disease Increases the Severity of Myocardial Infarction after Acute Ischemia-Reperfusion Injury in Mice

(1) Background: Increased risk of myocardial infarction (MI) has been linked to several inflammatory conditions, including inflammatory bowel disease (IBD). However, the relationship between IBD and MI remains unclear. Here, we implemented an original mouse model combining IBD and MI to determine IBD's impact on MI severity and the link between the two diseases. (2) Methods: An IBD model was established by dextran sulfate sodium (DSS) administration in drinking water, alone or with oral C. albicans (Ca) gavage. IBD severity was assessed by clinical/histological scores and intestinal/systemic inflammatory biomarker measurement. Mice were subjected to myocardial ischemia-reperfusion (IR), and MI severity was assessed by quantifying infarct size (IS) and serum cardiac troponin I (cTnI) levels. (3) Results: IBD mice exhibited elevated fecal lipocalin 2 (Lcn2) and IL-6 levels. DSS mice exhibited almost two-fold increase in IS compared to controls, with serum cTnI levels strongly correlated with IS. Ca inoculation tended to worsen DSS-induced systemic inflammation and IR injury, an observation which is not statistically significant. (4) Conclusions: This is the first proof-of-concept study demonstrating the impact of IBD on MI severity and suggesting mechanistic aspects involved in the IBD-MI connection. Our findings could pave the way for MI therapeutic approaches based on identified IBD-induced inflammatory mediators.

Snake Venom Components as Therapeutic Drugs in Ischemic Heart Disease

Ischemic heart disease (IHD), especially myocardial infarction (MI), is a leading cause of death worldwide. Although coronary reperfusion is the most straightforward treatment for limiting the MI size, it has nevertheless been shown to exacerbate ischemic myocardial injury. Therefore, identifying and developing therapeutic strategies to treat IHD is a major medical challenge. Snake venoms contain biologically active proteins and peptides that are of major interest for pharmacological applications in the cardiovascular system (CVS). This has led to their use for the development and design of new drugs, such as the first-in-class angiotensin-converting enzyme inhibitor captopril, developed from a peptide present in Bothrops jararaca snake venom. This review discusses the potential usefulness of snake venom toxins for developing effective treatments against IHD and related diseases such as hypertension and atherosclerosis. It describes their biological effects at the molecular scale, their mechanisms of action according to their different pharmacological properties, as well as their subsequent molecular pathways and therapeutic targets. The molecules reported here have either been approved for human medical use and are currently available on the drug market or are still in the clinical or preclinical developmental stages. The information summarized here may be useful in providing insights into the development of future snake venom-derived drugs.

Update on Angiotensin II Subtype 2 Receptor: Focus on Peptide and Nonpeptide Agonists

Angiotensin II (Ang II) is the most dominant effector component of the renin-angiotensin system (RAS) that generally acts through binding to two main classes of G protein-coupled receptors, namely Ang II subtype 1 receptor (AT1R) and angiotensin II subtype 2 receptor (AT2R). Despite some controversial reports, the activation of AT2R generally antagonizes the effects of Ang II binding on AT1R. Studying AT2R signaling, function, and its specific ligands in cell culture or animal studies has confirmed its beneficial effects throughout the body. These characteristics classify AT2R as part of the protective arm of the RAS that, along with functions of Ang (1-7) through Mas receptor signaling, modulates the harmful effects of Ang II on AT1R in the activated classic arm of the RAS. Although Ang II is the primary ligand for AT2R, we have summarized other natural or synthetic peptide and nonpeptide agonists with critical evaluation of their structure, mechanism of action, and biologic activity. SIGNIFICANCE STATEMENT: AT2R is one of the main components of the RAS and has a significant prospective for mediating the beneficial action of the RAS through its protective arm on the body's homeostasis. Targeting AT2R offers substantial clinical application possibilities for modulating various pathological conditions. This review provided concise information regarding the AT2R peptide and nonpeptide agonists and their potential clinical applications for various diseases.

Kinins and Kinin Receptors in Cardiovascular and Renal Diseases

This review addresses the physiological role of the kallikrein–kinin system in arteries, heart and kidney and the consequences of kallikrein and kinin actions in diseases affecting these organs, especially ischemic and diabetic diseases. Emphasis is put on pharmacological and genetic studies targeting kallikrein; ACE/kininase II; and the two kinin receptors, B1 (B1R) and B2 (B2R), distinguished through the work of Domenico Regoli and his collaborators. Potential therapeutic interest and limitations of the pharmacological manipulation of B1R or B2R activity in cardiovascular and renal diseases are discussed. This discussion addresses either the activation or inhibition of these receptors, based on recent clinical and experimental studies.

The Role of Natriuretic Peptides in the Regulation of Cardiac Tolerance to Ischemia/Reperfusion and Postinfarction Heart Remodeling

In the past 10 years, mortality from acute myocardial infarction has not decreased despite the widespread introduction of percutaneous coronary intervention. The reason for this situation is the absence in clinical practice of drugs capable of preventing reperfusion injury of the heart with high efficiency. In this regard, noteworthy natriuretic peptides (NPs) which have the infarct-limiting effect, prevent reperfusion cardiac injury, prevent adverse post-infarction remodeling of the heart. Atrial natriuretic peptide does not have the infarct-reducing effect in rats with alloxan-induced diabetes mellitus. NPs have the anti-apoptotic and anti-inflammatory effects. There is indirect evidence that NPs inhibit pyroptosis and autophagy. Published data indicate that NPs inhibit reactive oxygen species production in cardiomyocytes, aorta, heart, kidney and the endothelial cells. NPs can suppress aldosterone, angiotensin II, endothelin-1 synthesize and secretion. NPs inhibit the effects aldosterone, angiotensin II on the post-receptor level through intracellular signaling events. NPs activate guanylyl cyclase, protein kinase G and protein kinase A, and reduce phosphodiesterase 3 activity. NO-synthase and soluble guanylyl cyclase are involved in the cardioprotective effect of NPs. The cardioprotective effect of natriuretic peptides is mediated via activation of kinases (AMPK, PKC, PI3 K, ERK1/2, p70s6 k, Akt) and inhibition of glycogen synthase kinase 3β. The cardioprotective effect of NPs is mediated via sarcolemmal K_ATP channel and mitochondrial K_ATP channel opening. The cardioprotective effect of brain natriuretic peptide is mediated via MPT pore closing. The anti-fibrotic effect of NPs may be mediated through inhibition TGF-β1 expression. Natriuretic peptides can inhibit NF-κB activity and activate GATA. Hemeoxygenase-1 and peroxisome proliferator-activated receptor γ may be involved in the infarct-reducing effect of NPs. NPs exhibit the infarct-limiting effect in patients with acute myocardial infarction. NPs prevent post-infarction remodeling of the heart. To finally resolve the question of the feasibility of using NPs in AMI, a multicenter, randomized, blind, placebo-controlled study is needed to assess the effect of NPs on the mortality of patients after AMI.

Lebetin 2, a Snake Venom-Derived B-Type Natriuretic Peptide, Provides Immediate and Prolonged Protection against Myocardial Ischemia-Reperfusion Injury via Modulation of Post-Ischemic Inflammatory Response

Myocardial infarction (MI) followed by left ventricular (LV) remodeling is the most frequent cause of heart failure. Lebetin 2 (L2), a snake venom-derived natriuretic peptide, exerts cardioprotection during acute myocardial ischemia-reperfusion (IR) ex vivo. However, its effects on delayed consequences of IR injury, including post-MI inflammation and fibrosis have not been defined. Here, we determined whether a single L2 injection exerts cardioprotection in IR murine models in vivo, and whether inflammatory response to ischemic injury plays a role in L2-induced effects. We quantified infarct size (IS), fibrosis, inflammation, and both endothelial cell and cardiomyocyte densities in injured myocardium and compared these values with those induced by B-type natriuretic peptide (BNP). Both L2 and BNP reduced IS, fibrosis, and inflammatory response after IR, as evidenced by decreased leukocyte and proinflammatory M1 macrophage infiltrations in the infarcted area compared to untreated animals. However, only L2 increased anti-inflammatory M2-like macrophages. L2 also induced a higher density of endothelial cells and cardiomyocytes. Our data show that L2 has strong, acute, prolonged cardioprotective effects in post-MI that are mediated, at least in part, by the modulation of the post-ischemic inflammatory response and especially, by the enhancement of M2-like macrophages, thus reducing IR-induced necrotic and fibrotic effects.

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.

Neprilysin Inhibitors and Bradykinin

Bradykinin has important physiological actions related to the regulation of blood vessel tone and renal function, and protection from ischemia reperfusion injury. However, bradykinin also contributes to pathological states such as angioedema and inflammation. Bradykinin is metabolized by many different peptidases that play a major role in the control of bradykinin levels. Peptidase inhibitor therapies such as angiotensin converting enzyme (ACE) and neprilysin inhibitors increase bradykinin levels, and the challenge for such therapies is to achieve the beneficial cardiovascular and renal effects without the adverse consequences such as angioedema that may result from increased bradykinin levels. Neprilysin also metabolizes natriuretic peptides. However, despite the potential therapeutic benefit of increased natriuretic peptide and bradykinin levels, neprilysin inhibitor therapy has only modest efficacy in essential hypertension and heart failure. Initial attempts to combine neprilysin inhibition with inhibition of the renin angiotensin system led to the development of omapatrilat, a drug that combines ACE and neprilysin inhibition. However, omapatrilat produced an unacceptably high incidence of angioedema in patients with hypertension (2.17%) in comparison with the ACE inhibitor enalapril (0.68%), although angioedema incidence was less in patients with heart failure with reduced ejection fraction (HFrEF) treated with omapatrilat (0.8%), and not different from that for enalapril therapy (0.5%). More recently, LCZ696, a drug that combines angiotensin receptor blockade and neprilysin inhibition, was approved for the treatment of HFrEF. The approval of LCZ696 therapy for HFrEF represents the first approval of long-term neprilysin inhibitor administration. While angioedema incidence was acceptably low in HFrEF patients receiving LCZ696 therapy (0.45%), it remains to be seen whether LCZ696 therapy for other conditions such as hypertension is also accompanied by an acceptable incidence of angioedema.

Genetically increased angiotensin I-converting enzyme alters peripheral and renal vascular reactivity to angiotensin II and bradykinin in mice

Angiotensin I-converting enzyme (ACE) levels in humans are under strong genetic influence. Genetic variation in ACE has been linked to risk for and progression of cardiovascular and renal diseases. Causality has been documented in genetically modified mice, but the mechanisms underlying causality are not completely elucidated. To further document the vascular and renal consequences of a moderate genetic increase in ACE synthesis, we studied genetically modified mice carrying three copies of the ACE gene (three-copy mice) and littermate wild-type animals (two-copy mice). We investigated peripheral and renal vascular reactivity to angiotensin II and bradykinin in vivo by measuring blood pressure and renal blood flow after intravenous administration and also reactivity of isolated glomerular arterioles by following intracellular Ca2+ mobilization. Carrying three copies of the ACE gene potentiated the systemic and renal vascular responses to angiotensin II over the whole range of peptide concentration tested. Consistently, the response of isolated glomerular afferent arterioles to angiotensin II was enhanced in three-copy mice. In these mice, signaling pathways triggered by endothelial activation by bradykinin or carbachol in glomerular arterioles were also altered. Although the nitric oxide (NO) synthase (NOS)/NO pathway was not functional in arterioles of two-copy mice, in muscular efferent arterioles of three-copy mice NOS3 gene expression was induced and NO mediated the effect of bradykinin or carbachol. These data document new and unexpected vascular consequences of a genetic increase in ACE synthesis. Enhanced vasoconstrictor effect of angiotensin II may contribute to the risk for cardiovascular and renal diseases linked to genetically high ACE levels.

NEW & NOTEWORTHY A moderate genetic increase in angiotensin I-converting enzyme (ACE) in mice similar to the effect of the ACE gene D allele in humans unexpectedly potentiates the systemic and renal vasoconstrictor responses to angiotensin II. It also alters the endothelial signaling pathways triggered by bradykinin or carbachol in glomerular efferent arterioles.

The Renin-Angiotensin-Aldosterone System as a Therapeutic Target in Late Injury Caused by Ischemia-Reperfusion

Ischemia-reperfusion (I/R) injury is a well-known phenomenon that involves different pathophysiological processes. Connection in diverse systems of survival brings about cellular dysfunction or even apoptosis. One of the survival systems of the cells, to the assault caused by ischemia, is the activation of the renin-angiotensin-aldosterone system (also known as an axis), which is focused on activating diverse signaling pathways to favor adaptation to the decrease in metabolic supports caused by the hypoxia. In trying to adapt to the I/R event, great changes occur that unchain cellular dysfunction with the capacity to lead to cell death, which translates into a poor prognosis due to the progression of dysfunction of the cellular activity. The search for the understanding of the diverse therapeutic alternatives in molecular coupling could favor the prognosis and evolution of patients who are subject to the I/R process.

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.

Long-term neprilysin inhibition - implications for ARNIs

Neprilysin has a major role in both the generation and degradation of bioactive peptides. LCZ696 (valsartan/sacubitril, Entresto), the first of the new ARNI (dual-acting angiotensin-receptor-neprilysin inhibitor) drug class, contains equimolar amounts of valsartan, an angiotensin-receptor blocker, and sacubitril, a prodrug for the neprilysin inhibitor LBQ657. LCZ696 reduced blood pressure more than valsartan alone in patients with hypertension. In the PARADIGM-HF study, LCZ696 was superior to the angiotensin-converting enzyme inhibitor enalapril for the treatment of heart failure with reduced ejection fraction, and LCZ696 was approved by the FDA for this purpose in 2015. This approval was the first for chronic neprilysin inhibition. The many peptides metabolized by neprilysin suggest many potential consequences of chronic neprilysin inhibitor therapy, both beneficial and adverse. Moreover, LBQ657 might inhibit enzymes other than neprilysin. Chronic neprilysin inhibition might have an effect on angio-oedema, bronchial reactivity, inflammation, and cancer, and might predispose to polyneuropathy. Additionally, inhibition of neprilysin metabolism of amyloid-β peptides might have an effect on Alzheimer disease, age-related macular degeneration, and cerebral amyloid angiopathy. Much of the evidence for possible adverse consequences of chronic neprilysin inhibition comes from studies in animal models, and the relevance of this evidence to humans is unknown. This Review summarizes current knowledge of neprilysin function and possible consequences of chronic neprilysin inhibition that indicate a need for vigilance in the use of neprilysin inhibitor therapy.

Therapeutic modulation of tissue kallikrein expression

The kallikrein kinin system has cardioprotective actions and mediates in part the cardioprotection produced by angiotensin converting enzyme inhibitors and angiotensin type 1 receptor blockers. Additional approaches to exploit the cardioprotective effects of the kallikrein kinin system include the administration of tissue kallikrein and kinin receptor agonists. The renin inhibitor aliskiren was recently shown to increase cardiac tissue kallikrein expression and bradykinin levels, and to reduce myocardial ischemia-reperfusion injury by bradykinin B2 receptor- and angiotensin AT2 receptor-mediated mechanisms. Thus, aliskiren represents a prototype drug for the modulation of tissue kallikrein expression for therapeutic benefit.

The Interplay between the Renin Angiotensin System and Pacing Postconditioning Induced Cardiac Protection

Background

Accumulating evidence suggests a cardioprotective role of pacing postconditioning (PPC) maneuvers in animal models and more recently in humans. The procedure however remains to be optimized and its interaction with physiological systems remains to be further explored. The renin angiotensin system (RAS) plays a dual role in ischemia/reperfusion (I/R) injury. The interaction between RAS and PPC induced cardiac protection is however not clearly understood. We have recently demonstrated that angiotensin (1–7) via Mas receptor played a significant role in PPC mediated cardiac protection against I/R injury.

Objective

The objective of this study was to investigate the role of angiotensin converting enzyme (ACE)—chymase—angiotensin II (Ang II)—angiotensin receptor 1 (AT1) axes of RAS in PPC mediated cardiac protection.

Methods

Isolated rat hearts were subjected to I/R (control) or PPC in the presence or absence of Ang II, chymostatin (inhibitor of locally produced Ang II), ACE blocker (captopril) or AT1 antagonist (irbesartan). Hemodynamics data was computed digitally and infarct size was determined histologically using TTC staining and biochemically by measuring creatine kinase (CK) and lactate dehydrogenase levels.

Results

Cardiac hemodynamics were significantly (P<0.001) improved and infarct size and cardiac enzymes were significantly (P<0.001) reduced in hearts subjected to PPC relative to hearts subjected to I/R injury. Exogenous administration of Ang II did not affect I/R injury or PPC mediated protection. Nonetheless inhibition of endogenously synthesized Ang II protected against I/R induced cardiac damage yet did not block or augment the protective effects of PPC. The administration of AT1 antagonist did not alleviate I/R induced damage. Interestingly it abrogated PPC induced cardiac protection in isolated rat hearts. Finally, PPC induced protection and blockade of locally produced Ang II involved enhanced activation of ERK1/2 and Akt components of the reperfusion injury salvage kinase (RISK) pathway.

Conclusions

This study demonstrate a novel role of endogenously produced Ang II in mediating I/R injury and highlights the significance of AT1 signaling in PPC mediated cardiac protection in isolated rodents hearts ex vivo. The interaction between Ang II-AT1 and PPC appears to involve alterations in the activation state of ERK1/2 and Akt components of the RISK pathway.

Improvement of skin wound healing in diabetic mice by kinin B2 receptor blockade

Impaired skin wound healing is a major medical problem in diabetic subjects. Kinins exert a number of vascular and other actions limiting organ damage in ischaemia or diabetes, but their role in skin injury is unknown. We investigated, through pharmacological manipulation of bradykinin B1 and B2 receptors (B1R and B2R respectively), the role of kinins in wound healing in non-diabetic and diabetic mice. Using two mouse models of diabetes (streptozotocin-induced and db/db mice) and non-diabetic mice, we assessed the effect of kinin receptor activation or inhibition by subtype-selective pharmacological agonists (B1R and B2R) and antagonist (B2R) on healing of experimental skin wounds. We also studied effects of agonists and antagonist on keratinocytes and fibroblasts in vitro. Levels of Bdkrb1 (encoding B1R) and Bdkrb2 (encoding B2R) mRNAs increased 1-2-fold in healthy and wounded diabetic skin compared with in non-diabetic skin. Diabetes delayed wound healing. The B1R agonist had no effect on wound healing. In contrast, the B2R agonist impaired wound repair in both non-diabetic and diabetic mice, inducing skin disorganization and epidermis thickening. In vitro, B2R activation unbalanced fibroblast/keratinocyte proliferation and increased keratinocyte migration. These effects were abolished by co-administration of B2R antagonist. Interestingly, in the two mouse models of diabetes, the B2R antagonist administered alone normalized wound healing. This effect was associated with the induction of Ccl2 (encoding monocyte chemoattractant protein 1)/Tnf (encoding tumour necrosis factor α) mRNAs. Thus stimulation of kinin B2 receptor impairs skin wound healing in mice. B2R activation occurs in the diabetic skin and delays wound healing. B2R blockade improves skin wound healing in diabetic mice and is a potential therapeutic approach to diabetic ulcers.

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 effect of fimasartan, a new angiotensin receptor blocker, in a porcine model of acute myocardial infarction

Cardioprotective effect of fimasartan, a new angiotensin receptor blocker (ARB), was evaluated in a porcine model of acute myocardial infarction (MI). Fifty swine were randomized to group 1 (sham, n=10), group 2 (no angiotensin-converting enzyme inhibitor [ACEI] or ARB, n=10), group 3 (perindopril 2 mg daily, n=10), group 4 (valsartan 40 mg daily, n=10), or group 5 (fimasartan 30 mg daily, n=10). Acute MI was induced by occlusion of the left anterior descending artery for 50 min. Echocardiography, single photon emission computed tomography (SPECT), and F-18 fluorodeoxyglucose cardiac positron emission tomography (PET) were performed at baseline, 1 week, and 4 weeks. Iodine-123 meta-iodobenzylguanidine (MIBG) scan was done at 6 weeks for visualization of cardiac sympathetic activity. Left ventricular function and volumes at 4 weeks were similar between the 5 groups. No difference was observed in groups 2 to 5 in SPECT perfusion defect, matched and mismatched segments between SPECT and PET at 1 week and 4 weeks. MIBG scan showed similar uptake between the 5 groups. Pathologic analysis showed similar infarct size in groups 2 to 5. Infarct size reduction was not observed with use of fimasartan as well as other ACEI and ARB in a porcine model of acute MI.

Tissue kallikrein deficiency, insulin resistance, and diabetes in mouse and man

The kallikrein-kinin system has been suggested to participate in the control of glucose metabolism. Its role and the role of angiotensin-I-converting enzyme, a major kinin-inactivating enzyme, are however the subject of debate. We have evaluated the consequence of deficiency in tissue kallikrein (TK), the main kinin-forming enzyme, on the development of insulin resistance and diabetes in mice and man. Mice with inactivation of the TK gene were fed a high-fat diet (HFD) for 3 months, or crossed with obese, leptin-deficient (ob/ob) mice to generate double ob/ob-TK-deficient mutants. In man, a loss-of-function polymorphism of the TK gene (R53H) was studied in a large general population cohort tested for insulin resistance, the DESIR study (4843 participants, 9 year follow-up). Mice deficient in TK gained less weight on the HFD than their WT littermates. Fasting glucose level was increased and responses to glucose (GTT) and insulin (ITT) tolerance tests were altered at 10 and 16 weeks on the HFD compared with standard on the diet, but TK deficiency had no influence on these parameters. Likewise, ob-TK⁻/⁻ mice had similar GTT and ITT responses to those of ob-TK⁺/⁺ mice. TK deficiency had no effect on blood pressure in either model. In humans, changes over time in BMI, fasting plasma glucose, insulinemia, and blood pressure were not influenced by the defective 53H-coding TK allele. The incidence of diabetes was not influenced by this allele. These data do not support a role for the TK-kinin system, protective or deleterious, in the development of insulin resistance and diabetes.

Vasopressor meets vasodepressor: The AT1-B2 receptor heterodimer

The AT1 receptor for the vasopressor angiotensin II is one of the most important drug targets for the treatment of cardiovascular diseases. Sensitization of the AT1 receptor system is a common feature contributing to the pathogenesis of many cardiovascular disorders but underlying mechanisms are not fully understood. More than a decade ago, evidence was provided for control of AT1R activation by heterodimerization with the B2 receptor for the vasodepressor peptide, bradykinin, a physiological counterpart of the vasoconstrictor angiotensin II. AT1-B2 receptor heterodimerization was shown to enhance AT1R-stimulated signaling under pathophysiological conditions such as experimental and human pregnancy hypertension. Notably, AT1R signal sensitization of patients with preeclampsia hypertension was attributed to AT1R-B2R heterodimerization. Vice versa, transgenic mice lacking the AT1-B2 receptor heterodimer due to targeted deletion of the B2R gene showed a significantly reduced AT1R-stimulated vasopressor response compared to transgenic mice with abundant AT1R-B2R heterodimerization. Biophysical methods such as BRET and FRET confirmed those data by demonstrating efficient AT1-B2 receptor heterodimerization in transfected cells and transgenic mice. Recently, a study on AT1R-specific biased agonism directed the focus to the AT1-B2 receptor heterodimer again. The β-arrestin-biased [Sar1,Ile4,Ile8]-angiotensin II promoted not only the recruitment of β-arrestin to the AT1R but also stimulated the down-regulation of the AT1R-associated B2 receptor by co-internalization. Thereby specific targeting of the AT1R-B2R heterodimer became feasible and could open the way to a new class of drugs, which specifically interfere with pathological angiotensin II-AT1 receptor system activation.

Aliskiren reduces myocardial ischemia-reperfusion injury by a bradykinin B2 receptor- and angiotensin AT2 receptor-mediated mechanism

Angiotensin-converting enzyme inhibitors and angiotensin AT1 receptor blockers reduce myocardial ischemia-reperfusion injury via bradykinin B2 receptor- and angiotensin AT2 receptor-mediated mechanisms. The renin inhibitor aliskiren increases cardiac tissue kallikrein and bradykinin levels. In the present study, we investigated the effect of aliskiren on myocardial ischemia-reperfusion injury and the roles of B2 and AT2 receptors in this effect. Female Sprague-Dawley rats were treated with aliskiren (10 mg/kg per day) and valsartan (30 mg/kg per day), alone or in combination, together with the B2 receptor antagonist icatibant (0.5 mg/kg per day) or the AT2 receptor antagonist PD123319 (30 mg/kg per day), for 4 weeks before myocardial ischemia-reperfusion injury. Aliskiren increased cardiac bradykinin levels and attenuated valsartan-induced increases in plasma angiotensin II levels. In vehicle-treated rats, myocardial infarct size (% area at risk, mean±SEM, n=7-13) was 43±3%. This was reduced to a similar extent by aliskiren, valsartan, and their combination to 24±3%, 25±3%, and 22±2%, respectively. Icatibant reversed the cardioprotective effects of aliskiren and the combination of aliskiren plus valsartan, but not valsartan alone, indicating that valsartan-induced cardioprotection was not mediated by the B2 receptor. PD123319 reversed the cardioprotective effects of aliskiren, valsartan, and the combination of aliskiren plus valsartan. Aliskiren protects the heart from myocardial ischemia-reperfusion injury via a B2 receptor- and AT2 receptor-mediated mechanism, whereas cardioprotection by valsartan is mediated via the AT2 receptor. In addition, aliskiren attenuates valsartan-induced increases in angiotensin II levels, thus preventing AT2 receptor-mediated cardioprotection by valsartan.

Genetic manipulation and genetic variation of the kallikrein-kinin system: impact on cardiovascular and renal diseases

Genetic manipulation of the kallikrein-kinin system (KKS) in mice, with either gain or loss of function, and study of human genetic variability in KKS components which has been well documented at the phenotypic and genomic level, have allowed recognizing the physiological role of KKS in health and in disease. This role has been especially documented in the cardiovascular system and the kidney. Kinins are produced at slow rate in most organs in resting condition and/or inactivated quickly. Yet the KKS is involved in arterial function and in renal tubular function. In several pathological situations, kinin production increases, kinin receptor synthesis is upregulated, and kinins play an important role, whether beneficial or detrimental, in disease outcome. In the setting of ischemic, diabetic or hemodynamic aggression, kinin release by tissue kallikrein protects against organ damage, through B2 and/or B1 bradykinin receptor activation, depending on organ and disease. This has been well documented for the ischemic or diabetic heart, kidney and skeletal muscle, where KKS activity reduces oxidative stress, limits necrosis or fibrosis and promotes angiogenesis. On the other hand, in some pathological situations where plasma prekallikrein is inappropriately activated, excess kinin release in local or systemic circulation is detrimental, through oedema or hypotension. Putative therapeutic application of these clinical and experimental findings through current pharmacological development is discussed in the chapter.

Angiotensin type 1a receptor-deficient mice develop diabetes-induced cardiac dysfunction, which is prevented by renin-angiotensin system inhibitors

Background

Diabetes-induced organ damage is significantly associated with the activation of the renin-angiotensin system (RAS). Recently, several studies have demonstrated a change in the RAS from an extracellular to an intracellular system, in several cell types, in response to high ambient glucose levels. In cardiac myocytes, intracellular angiotensin (ANG) II synthesis and actions are ACE and AT₁ independent, respectively. However, a role of this system in diabetes-induced organ damage is not clear.

Methods

To determine a role of the intracellular ANG II in diabetic cardiomyopathy, we induced diabetes using streptozotocin in AT_1a receptor deficient (AT_1a-KO) mice to exclude any effects of extracellular ANG II. Further, diabetic animals were treated with a renin inhibitor aliskiren, an ACE inhibitor benazeprilat, and an AT₁ receptor blocker valsartan.

Results

AT_1a-KO mice developed significant diastolic and systolic dysfunction following 10 wks of diabetes, as determined by echocardiography. All three drugs prevented the development of cardiac dysfunction in these animals, without affecting blood pressure or glucose levels. A significant down regulation of components of the kallikrein-kinin system (KKS) was observed in diabetic animals, which was largely prevented by benazeprilat and valsartan, while aliskiren normalized kininogen expression.

Conclusions

These data indicated that the AT_1a receptor, thus extracellular ANG II, are not required for the development of diabetic cardiomyopathy. The KKS might contribute to the beneficial effects of benazeprilat and valsartan in diabetic cardiomyopathy. A role of intracellular ANG II is suggested by the inhibitory effects of aliskiren, which needs confirmation in future studies.

Pathophysiology of genetic deficiency in tissue kallikrein activity in mouse and man

Study of mice rendered deficient in tissue kallikrein (TK) by gene inactivation and human subjects partially deficient in TK activity as consequence of an active site mutation has allowed recognising the physiological role of TK and its peptide products kinins in arterial function and in vasodilatation, in both species. TK appears as the major kinin forming enzyme in arteries, heart and kidney. Non-kinin mediated actions of TK may occur in epithelial cells in the renal tubule. In basal condition, TK deficiency induces mild defective phenotypes in the cardiovascular system and the kidney. However, in pathological situations where TK synthesis is typically increased and kinins are produced, TK deficiency has major, deleterious consequences. This has been well documented experimentally for cardiac ischaemia, diabetes renal disease, peripheral ischaemia and aldosterone-salt induced hypertension. These conditions are all aggravated by TK deficiency. The beneficial effect of ACE/kininase II inhibitors or angiotensin II AT1 receptor antagonists in cardiac ischaemia is abolished in TK-deficient mice, suggesting a prominent role for TK and kinins in the cardioprotective action of these drugs. Based on findings made in TK-deficient mice and additional evidence obtained by pharmacological or genetic inactivation of kinin receptors, development of novel therapeutic approaches relying on kinin receptor agonism may be warranted.

Valsartan attenuates oxidative stress and NF-κB activation and reduces myocardial apoptosis after ischemia and reperfusion

Myocardial apoptosis is primarily triggered during reperfusion. Various mechanisms are involved, including oxidative stress which activates the translocation of nuclear factor-kappa B (NF-κB) and stimulates the release of tumor necrosis factor-alpha (TNF-α). However, the relative contribution of the renin angiotensin system (RAS) to the development of myocardial apoptosis during reperfusion remains unknown. In the present study, we examined whether inhibition of RAS with Valsartan, an Angiotensin II 1 receptor (AT1) antagonist, could reduce apoptosis during reperfusion. We constructed a rat model of myocardial ischemia reperfusion injury. Rats were pretreated with Valsartan for 2 weeks, and then subjected to 30 min ischemia and 4h reperfusion. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). Levels of malondialdehyde (MDA), superoxide dismutase (SOD), TNF-α, and caspase-3 were detected by ELISA. NF-κB, Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase expression was assessed by Western blot analysis. Valsartan inhibited apoptosis (TUNEL staining) in ischemic myocardium (P<0.05), consistent with reduced caspase-3 activity. Valsartan also inhibited of NF-κB translocation to nucleus (P<0.05), and decreased plasma TNF-α levels (P<0.05). Valsartan pretreatment suppressed MDA content and preserved SOD activity, consistent with reduced NADPH oxidase expression (P<0.01). These data provided substantial evidence that RAS was involved in NF-κB activation, mediated by AT1 dependent oxidative stress; thus, RAS might ultimately promote myocardial apoptosis during reperfusion pathogenesis.

Influence of ramiprilat and losartan on ischemia reperfusion injury in rat hearts

Hypothesis/introduction: Our aim was to investigate whether a non-hypotensive dose of ramiprilat and losartan has myocardial protective effects during myocardial ischemia/reperfusion in vivo.

Materials and methods: Three groups of rats were given 10 mg/kg per day of losartan for one (L-1W), four (L-4W) or 10 (L-10W) weeks. Another three groups were given 50 µg/kg per day of ramiprilat for one (R-1W), four (R-4W) or 10 (R-10W) weeks. The animals underwent 30 min of left anterior descending artery occlusion and subsequent reperfusion for 120 min.

Results: Myocardial infarct size (IS) was reduced in R-1W (28.4 ± 6.3%, p < 0.001), R-4W (27.8 ± 7.4, p < 0.001), L-4W (31.8 ± 6%, p < 0.05) and L-10W (25.3 ± 5.7, p < 0.001) groups compared with a saline group (48.3 ± 7.8%). A significant reduction in the number of ventricular ectopic beats (VEBs) was noted in groups R-1W (209 ± 41, p < 0.01), R-4W (176 ± 39, p < 0.01), L-4W (215 ± 52, p < 0.05) and L-10W (191 ± 61, p < 0.01 vs. saline 329 ± 48). The incidence of irreversible ventricular fibrillation (VF) and mortality were decreased significantly only in L-10W group.

There were no significant decreases in episodes of VT, the incidence of irreversible VF and mortality in all of the groups treated with ramiprilat.

Conclusion: These data indicate that losartan and ramiprilat protect the heart against ischemia/reperfusion injury independently of their hemodynamic effects but in a time-dependent manner.

Hypertensive left ventricular hypertrophy risk: beyond adaptive cardiomyocytic hypertrophy

The heart is a remarkably adaptive organ, capable of increasing its minute output and overcoming short-term or prolonged pressure overload. The structural response, in addition to the foregoing functional demands, is that of myocardial hypertrophy. Then, why should an adaptive response increase cardiovascular risk in hypertensive patients with left ventricular hypertrophy (LVH)? Evidence shows that the functional performance of hypertrophied cardiomyocytes is impaired, and that additional alterations develop in cardiomyocytes themselves, the extracellular matrix and the intramyocardial vasculature, leading to myocardial remodelling and providing the basis for the adverse prognosis associated with pathological LVH in hypertensive patients (i.e., hypertensive heart disease, HHD). As molecular information accumulates, the pathophysiological understanding and the clinical approach to HHD are changing. The time has come to develop novel diagnostic and therapeutic strategies aimed at improving the prognosis of HHD on the basis of reversing or even preventing the aforementioned changes in the ventricular myocardium.

Genetically determined angiotensin converting enzyme level and myocardial tolerance to ischemia

Angiotensin I-converting enzyme (ACE; kininase II) levels in humans are genetically determined. ACE levels have been linked to risk of myocardial infarction, but the association has been inconsistent, and the causality underlying it remains undocumented. We tested the hypothesis that genetic variation in ACE levels influences myocardial tolerance to ischemia. We studied ischemia-reperfusion injury in mice bearing 1 (ACE1c), 2 (ACE2c, wild type), or 3 (ACE3c) functional copies of the ACE gene and displaying an ACE level range similar to humans. Infarct size in ACE1c was 29% lower than in ACE2c (P<0.05). Pretreatment with a kinin B2 receptor antagonist suppressed this reduction. In ACE3c, infarct size was the same as in ACE2c. But ischemic preconditioning, which reduced infarct size in ACE2c (-63%, P<0.001) and ACE1c (-52%, P<0.05), was not efficient in ACE3c (-2%, NS, P<0.01 vs. ACE2c). In ACE3c, ischemic preconditioning did not decrease myocardial inflammation or cardiomyocyte apoptosis. Pretreatment with a renin inhibitor had no cardioprotective effect in ACE2c, but in ACE3c partially restored (38%) the cardioprotection of ischemic preconditioning. Thus, a modest genetic increase in ACE impairs myocardial tolerance to ischemia. ACE level plays a critical role in cardiac ischemia, through both kinin and angiotensin mediated mechanisms.

Genetically determined angiotensin converting enzyme level and myocardial tolerance to ischemia

Angiotensin I-converting enzyme (ACE; kininase II) levels in humans are genetically determined. ACE levels have been linked to risk of myocardial infarction, but the association has been inconsistent, and the causality underlying it remains undocumented. We tested the hypothesis that genetic variation in ACE levels influences myocardial tolerance to ischemia. We studied ischemia-reperfusion injury in mice bearing 1 (ACE1c), 2 (ACE2c, wild type), or 3 (ACE3c) functional copies of the ACE gene and displaying an ACE level range similar to humans. Infarct size in ACE1c was 29% lower than in ACE2c (P<0.05). Pretreatment with a kinin B2 receptor antagonist suppressed this reduction. In ACE3c, infarct size was the same as in ACE2c. But ischemic preconditioning, which reduced infarct size in ACE2c (-63%, P<0.001) and ACE1c (-52%, P<0.05), was not efficient in ACE3c (-2%, NS, P<0.01 vs. ACE2c). In ACE3c, ischemic preconditioning did not decrease myocardial inflammation or cardiomyocyte apoptosis. Pretreatment with a renin inhibitor had no cardioprotective effect in ACE2c, but in ACE3c partially restored (38%) the cardioprotection of ischemic preconditioning. Thus, a modest genetic increase in ACE impairs myocardial tolerance to ischemia. ACE level plays a critical role in cardiac ischemia, through both kinin and angiotensin mediated mechanisms.

Effects of protein coding polymorphisms in the kallikrein 1 gene on baseline blood pressure and antihypertensive response to irbesartan in Chinese hypertensive patients

The aim of this study was to determine the association between coding variants in the human tissue kallikrein 1 (KLK1) gene and baseline blood pressure (BP) and antihypertensive response to irbesartan treatment in Chinese hypertensive patients. A total of 1061 hypertensives were recruited and received daily oral dosage of 150 mg irbesartan for 4 weeks. Predose BPs, BPs and blood irbesartan concentrations at postdose on the 28th day were all measured. Common functional single-nucleotide polymorphisms (SNPs) in the KLK1 gene were genotyped. On the basis of the HapMap data of Han Chinese in the Beijing population, two non-synonymous polymorphisms with minor allele frequency>0.1, SNP rs5517 (Glu162Lys) and rs5516 (Gln121Glu), were selected. Those with GG genotype in the rs5516 locus had higher average baseline systolic BP (SBP) than CC subjects (β±s.e.: 5.0±2.3, P=0.033); and no associations of rs5517 with baseline BP (diastolic BP (DBP) and SBP) and BP responses, or rs5516 with baseline DBP and BP response were observed. In a haplotype-based association test for the KLK1 gene, the Haplo-special score analyses identified that haplotype AG was marginally associated with SBP response (specific score: 1.75 for P=0.08), but not with DBP response. We did not find any associations between haplotypes (GC and AC) and BP responses. The Haplo-GLM analyses showed that, compared with haplotype GC subjects, the subjects with haplotype AG had a marginally greater SBP response (adjusted β±s.e.: 1.81±0.97, P=0.06), but DBP response did not differ. This study suggests that rs5516 in the KLK1 gene may be involved in the development of essential hypertension and in the regulation of SBP-lowering response to irbesartan in Chinese hypertensives.

Recombinant adeno-associated virus-mediated human kallikrein gene therapy protects against hypertensive target organ injuries through inhibiting cell apoptosis

AIM

Overexpression of human tissue kallikrein (HK), mediated by recombinant adeno-associated virus (rAAV), decreased blood pressure in spontaneous hypertensive rats (SHRs) and reduced injury to the heart, aorta and kidney. In this study, we used both an in vivo animal model and in vitro cell culture system to investigate whether rAAV-mediated HK gene therapy protects against organ damage by inhibiting cell apoptosis.

METHODS

rAAV encoding HK (rAAV-HK) or LacZ (rAAV-lacZ) were delivered as a control to spontaneously hypertensive rats (SHRs) and cultured human embryonic kidney (HEK) 293 cells.

RESULTS

Treatment with rAAV-HK decreased cell apoptosis in the target organs of SHRs and also inhibited lipopolysaccharide (LPS)-induced HEK 293 apoptosis. The rAAV-HK delivery system also increased the levels of apoptosis-inhibiting proteins bcl-2 and bcl-x(L), and decreased the level of Bax and the activity of caspase 3, two promoters of apoptosis. In addition to its role in the inhibition of apoptosis, rAAV-HK also activated the cell survival and proliferation signaling pathways ERK1/2 and PI3K/AKT.

CONCLUSION

rAAV-mediated HK gene delivery has multiple therapeutic possibilities for treating hypertension, not only by decreasing blood pressure, but also by directly inhibiting end-organ damage.

Genetic deficiency in tissue kallikrein activity in mouse and man: effect on arteries, heart and kidney

Tissue kallikrein (KLK1) is a kinin-forming serine protease synthesized in many organs including arteries and kidney. Study of the physiological role of KLK1 has benefited from the availability of mouse and human genetic models of KLK1 deficiency, through engineering of KLK1 mouse mutants and discovery of a major polymorphism in the human KLK1 gene that induces a loss of enzyme activity. Studies in KLK1-deficient mice and human subjects partially deficient in KLK1 have documented its critical role in arterial function in both species. KLK1 is also involved in the control of ionic transport in the renal tubule, an action that may not be kinin-mediated. Studies of experimental diseases in KLK1-deficient mice have revealed cardio- and nephro-protective effects of KLK1 and kinins in acute cardiac ischemia, post-ischemic heart failure, and diabetes. Potential clinical and therapeutic developments are discussed.

The intracellular renin-angiotensin system: implications in cardiovascular remodeling

PURPOSE OF REVIEW

The renin-angiotensin system, traditionally viewed as a circulatory system, has significantly expanded in the last two decades to include independently regulated local systems in several tissues, newly identified active products of angiotensin II, and new receptors and functions of renin-angiotensin system components. In spite of our increased understanding of the renin-angiotensin system, a role of angiotensin II in cardiac hypertrophy, through direct effects on cardiovascular tissue, is still being debated. Here, we address the cardiovascular effects of angiotensin II and the role an intracellular renin-angiotensin system might play.

RECENT FINDINGS

Recent studies have shown that cardiac myocytes, fibroblasts and vascular smooth muscle cells synthesize angiotensin II intracellularly. Some conditions, such as high glucose, selectively increase intracellular generation and translocation of angiotensin II to the nucleus. Intracellular angiotensin II regulates the expression of angiotensinogen and renin, generating a feedback loop. The first reaction of intracellular angiotensin II synthesis is catalyzed by renin or cathepsin D, depending on the cell type, and chymase, not angiotensin-converting enzyme, catalyzes the second step.

SUMMARY

These studies suggest that the intracellular renin-angiotensin system is an important component of the local system. Alternative mechanisms of angiotensin II synthesis and action suggest a need for novel therapeutic agents to block the intracellular renin-angiotensin system.

Cardioprotection and kallikrein-kinin system in acute myocardial ischaemia in mice

1. Acute myocardial ischaemia and reperfusion trigger cardioprotective mechanisms that tend to limit myocardial injury. These cardioprotective mechanisms remain for a large part unknown, but can be potentiated by performing ischaemic preconditioning or by administering drugs such as angiotensin-I-converting enzyme (kininase II) inhibitors (ACEI). 2. This brief review summarizes the findings concerning the role of tissue kallikrein (TK), a major kinin-forming enzyme, kinins and kinin receptors in the cardioprotection afforded by ischaemic preconditioning (IPC) or by pharmacological postconditioning by drugs originally targeted at the renin-angiotensin system, ACEI and type 1 angiotensin-II receptor blockers (ARB) in acute myocardial ischaemia. Myocardial ischaemia was induced by left coronary occlusion and was followed after 30 min by a 3 h reperfusion period (IR), performed in vivo in mice. The role of the kallikrein-kinin system (KKS) was studied by using genetically engineered mice deficient in TK gene and their wild-type littermates, or by blocking B1 or B2 bradykinin receptors in wild-type mice using selective pharmacological antagonists. 3. Ischaemic preconditioning (three cycles: 3 min occlusion/5 min reperfusion) enhances the ability of the heart of wild-type mice to tolerate IR. Tissue kallikrein plays a major role in the cardioprotective effect afforded by IPC, which is largely reduced in TK-deficient mice. The B2 receptor is the main kinin receptor involved in the cardioprotective effect of IPC. 4. Tissue kallikrein is also required for the cardioprotective effects of pharmacological postconditioning with ACEI (ramiprilat) or ARB (losartan), which are abolished for both classes of drugs in TK-deficient mice. The B2 receptor mediates the cardioprotective effects of these drugs. Activation of angiotensin-II type 2 (AT2) receptor is involved in the cardioprotective effects of losartan, suggesting a functional coupling between AT2 receptor and TK during angiotensin-II type 1 (AT1) receptor blockade. 5. The demonstration of a cardioprotective effect of the KKS in acute myocardial ischaemia involving TK and the B2 receptor and playing a major role in IPC or pharmacological postconditioning by ACEI or ARB, suggests a potential therapeutic approach based on pharmacological activation of the B2 receptor.