Angiotensin I-converting enzyme inhibitors block protein kinase C epsilon by activating bradykinin B1 receptors in human endothelial cells

Perindopril prevents development of obesity and hypertension in middle aged diet-induced obese rat models of metabolic syndrome

AIMS

The therapeutic properties of anti-hypertensive medications that extend beyond blood pressure lowering have started to become important clinical targets in recent years. This study aimed to assess the cardioprotective effects of perindopril in attenuating complications associated with metabolic syndrome in diet induced obese rats.

MAIN METHODS

Male Wistar-Kyoto (WKY) rats aged 16 weeks were fed either standard rat chow (SC) or given a high-fat-high-carbohydrate (HFHC) diet for 20 weeks. Perindopril treatment (1 mg/kg/day) was administered to a subset of WKY rats commencing at week 8 of the 20 week HFHC feeding period. Body weights, food, water and energy intakes, blood pressure, heart rate and glucose tolerance were measured throughout the treatment period. Oxidative stress and inflammatory markers, lipid levels, cardiac collagen deposition, vascular function, aortic and cardiac electrical function were examined after the treatment.

KEY FINDINGS

WKY rats developed metabolic syndrome after 20 weeks of HFHC feeding, evidenced by the presence of abdominal obesity, dyslipidaemia, glucose intolerance and hypertension. Perindopril treatment prevented the development of obesity and hypertension in WKY-HFHC. Perindopril improved blood lipid profiles in HFHC rats with decreases in LDL cholesterol, triglycerides and total cholesterol. Type I collagen levels were decreased in WKY-HFHC rats along with decreases in left ventricle mass. Perindopril treated rats also showed improved cardiac electrical function indicated by decreases in action potential at 90 % of repolarisation in WKY-HFHC rats.

SIGNIFICANCE

These results show that perindopril has a profound effect on preventing the development of metabolic syndrome in animals fed a HFHC diet.

Pharmacotherapy and analysis of gaseous mediators in hypertensive patients

OBJECTIVE To evaluate the effect of using antihypertensive classes of drugs of the calcium channel antagonists and inhibitors of angiotensin-converting enzyme in plasma concentrations of hydrogen sulfide and nitric oxide in patients with hypertension. METHODS Cross-sectional study with quantitative approach conducted with hypertensive patients in use of antihypertensive classes of drugs: angiotensin-converting enzyme inhibitors or calcium channel antagonists. RESULTS It was found that the concentration of plasma nitric oxide was significantly higher in hypertensive patients that were in use of angiotensin-converting enzyme inhibitors (p<0.03) and the hydrogen sulphide concentration was significantly higher in hypertensive plasma in use of calcium channel antagonists (p<0.002). CONCLUSION The findings suggest that these medications have as additional action mechanism the improvement of endothelial dysfunction by elevate plasma levels of vasodilatory substances.

ACE inhibition enhances bradykinin relaxations through nitric oxide and B1 receptor activation in bovine coronary arteries

Bradykinin causes vascular relaxations through release of endothelial relaxing factors including prostacyclin, nitric oxide (NO) and epoxyeicosatrienoic acids (EETs). Bradykinin is metabolized by angiotensin converting enzyme (ACE) and ACE inhibition enhances bradykinin relaxations. Our goal was to characterize the role of bradykinin receptors and endothelial factors in ACE inhibitor-enhanced relaxations in bovine coronary arteries. In U46619 preconstricted arteries, bradykinin (10-11-10-8m) caused concentration-dependent relaxations (maximal relaxation ≥100%, log EC50=-9.8±0.1). In the presence of the NO synthase inhibitor, N-nitro-L-arginine (L-NA, 30 μm) and the cyclooxygenase inhibitor, indomethacin (10 μm), relaxations were reduced by an inhibitor of EET synthesis, miconazole (10 μm) (maximal relaxation=55±10%). Bradykinin relaxations were inhibited by the bradykinin 2 (B2) receptor antagonist, D-Arg0-Hyp3-Thi5,8-D-Phe7-bradykinin (1 μm) (log EC50=-8.5±0.1) but not altered by the B1 receptor antagonist, des-Arg9[Leu8]bradykinin (1 μm). Mass spectrometric analysis of bovine coronary artery bradykinin metabolites revealed a time-dependent increase in bradykinin (1-5) and (1-7) suggesting metabolism by ACE. ACE inhibition with captopril (50 μm) enhanced bradykinin relaxations (log EC50=-10.3±0.1). The enhanced relaxations were eliminated by L-NA or the B1 receptor antagonist but not the B2 receptor antagonist. Our results demonstrate that ACE inhibitor-enhanced bradykinin relaxations of bovine coronary arteries occur through endothelial cell B1 receptor activation and NO.

A novel pathway for receptor-mediated post-translational activation of inducible nitric oxide synthase

Inducible nitric oxide synthase (iNOS) is a major source of nitric oxide during inflammation whose activity is thought to be controlled primarily at the expression level. The B1 kinin receptor (B1R) post-translationally activates iNOS beyond its basal activity via extracellular signal regulated kinase (ERK)-mediated phosphorylation of Ser(745) . Here we identified the signalling pathway causing iNOS activation in cytokine-treated endothelial cells or HEK293 cells transfected with iNOS and B1R. To allow kinetic measurements of nitric oxide release, we used a sensitive porphyrinic microsensor (response time = 10 msec.; 1 nM detection limit). B1Rs signalled through Gαi coupling as ERK and iNOS activation were inhibited by pertussis toxin. Furthermore, transfection of constitutively active mutant Gαi Q204L but not Gαq Q209L resulted in high basal iNOS-derived nitric oxide. G-βγ subunits were also necessary as transfection with the β-adrenergic receptor kinase C-terminus inhibited the response. B1R-dependent iNOS activation was also inhibited by Src family kinase inhibitor PP2 and trans-fection with dominant negative Src. Other ERK-MAP kinase members were involved as the response was inhibited by dominant negative H-Ras, Raf kinase inhibitor, ERK activation inhibitor and MEK inhibitor PD98059. In contrast, PI3 kinase inhibitor LY94002, calcium chelator 1,2-bis-(o-Aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetraacetoxymethyl ester (BAPTA-AM), protein kinase C inhibitor calphostin C and protein kinase C activator PMA had no effect. Angiotensin converting enzyme inhibitor enalaprilat also directly activated B1Rs to generate high output nitric oxide via the same pathway. These studies reveal a new mechanism for generating receptor-regulated high output nitric oxide in inflamed endothelium that may play an important role in the development of vascular inflammation.

Differential regulation of inducible and endothelial nitric oxide synthase by kinin B1 and B2 receptors

Kinins are vasoactive peptides that play important roles in cardiovascular homeostasis, pain and inflammation. After release from their precursor kininogens, kinins or their C-terminal des-Arg metabolites activate two distinct G protein-coupled receptors (GPCR), called B2 (B2R) or B1 (B1R). The B2R is expressed constitutively with a wide tissue distribution. In contrast, the B1R is not expressed under normal conditions but is upregulated by tissue insult or inflammatory mediators. The B2R is considered to mediate many of the acute effects of kinins while the B1R is more responsible for chronic responses in inflammation. Both receptors can couple to Galphai and Galphaq families of G proteins to release mediators such as nitric oxide (NO), arachidonic acid, prostaglandins, leukotrienes and endothelium-derived hyperpolarizing factor and can induce the release of other inflammatory agents. The focus of this review is on the different transduction events that take place upon B2R and B1R activation in human endothelial cells that leads to generation of NO via activation of different NOS isoforms. Importantly, B2R-mediated eNOS activation leads to a transient ( approximately 5min) output of NO in control endothelial cells whereas in cytokine-treated endothelial cells, B1R activation leads to very high and prolonged ( approximately 90min) NO production that is mediated by a novel signal transduction pathway leading to post-translational activation of iNOS.

Beta-arrestin 2 is required for B1 receptor-dependent post-translational activation of inducible nitric oxide synthase

A major source of "high-output" NO in inflammation is inducible nitric oxide synthase (iNOS). iNOS is primarily transcriptionally regulated and is thought to function as an uncontrolled generator of high NO. We found that iNOS in cytokine-stimulated human lung microvascular endothelial cells (HLMVECs) is highly regulated post-translationally via activation of the B1 kinin G protein-coupled receptor (B1R). We report here that B1R-mediated iNOS activation was significantly inhibited by knockdown of beta-arrestin 2 with siRNA in cytokine-treated HLMVECs or HEK293 cells transfected with iNOS and B1R. In contrast, beta-arrestin 1 siRNA had no effect. The prolonged phase of B1R-dependent ERK activation was also inhibited by beta-arrestin 2 knockdown. Furthermore, robust ERK activation by the epidermal growth factor receptor (a beta-arrestin 2 independent pathway) had no effect on iNOS-derived NO production. beta-arrestin 2 and iNOS coimmunoprecipitated, and there was significant fluorescence resonance energy transfer between CFP-iNOS and beta-arrestin 2-YFP (but not beta-arrestin 1-YFP) that increased 3-fold after B1R stimulation. These data show that beta-arrestin 2 mediates B1R-dependent high-output NO by scaffolding iNOS and ERK to allow post-translational activation of iNOS. This could play a critical role in mediating endothelial function in inflammation.

Angiotensin I-converting enzyme inhibitors are allosteric enhancers of kinin B1 and B2 receptor function

The beneficial effects of angiotensin I-converting enzyme (ACE) inhibitors go beyond the inhibition of ACE to decrease angiotensin (Ang) II or increase kinin levels. ACE inhibitors also affect kinin B1 and B2 receptor (B1R and B2R) signaling, which may underlie some of their therapeutic usefulness. They can indirectly potentiate the actions of bradykinin (BK) and ACE-resistant BK analogs on B2Rs to elevate arachidonic acid and NO release in laboratory experiments. Studies indicate that ACE inhibitors and some Ang metabolites increase B2R functions as allosteric enhancers by inducing a conformational change in ACE. This is transmitted to B2Rs via heterodimerization with ACE on the plasma membrane of cells. ACE inhibitors are also agonists of the B1R, at a Zn-binding sequence on the second extracellular loop that differs from the orthosteric binding site of the des-Arg-kinin peptide ligands. Thus, ACE inhibitors act as direct allosteric B1R agonists. When ACE inhibitors enhance B2R and B1R signaling, they augment NO production. Enhancement of B2R signaling activates endothelial NO synthase, yielding a short burst of NO; activation of B1Rs results in a prolonged high output of NO by inducible NO synthase. These actions, outside inhibiting peptide hydrolysis, may contribute to the pleiotropic therapeutic effects of ACE inhibitors in various cardiovascular disorders.

Lack of direct interaction between enalaprilat and the kinin B1 receptors

It has been recently proposed that the second extracellular loop of the human bradykinin (BK) B1 receptor (B1R) contains a conserved HExxH motif also present in peptidases possessing a Zn2+ prosthetic group, such as angiotensin converting enzyme (ACE), and that ACE inhibitors directly activate B1R signaling in endothelial cells. However, the binding of ACE inhibitors to the B1Rs has never been directly evaluated. Information about binding of a radiolabeled inhibitor to natural or recombinant ACE in intact cells (physiologic ionic composition) was also collected. We used the tritiated form of an ACE inhibitor previously proposed to activate the B1R, enalaprilat, to address these questions using recombinant human B1Rs and naturally expressed or recombinant ACE. [3H]Lys-des-Arg9-BK bound to the human recombinant B1Rs with high affinity (KD 0.35 nM) in HEK 293a cells. [3H]Enalaprilat (0.25-10 nM) did not bind to cells expressing recombinant human B1R, but bound with a subnanomolar affinity to recombinant ACE or to naturally expressed ACE in human umbilical vein endothelial cells. The radioligand was further validated using a binding competition assay that involved unlabeled ACE inhibitors or their prodrug forms in endothelial cells. Membranes of HEK 293a cells that expressed B1Rs did not hydrolyze hippuryl-glycylglycine (an ACE substrate). Enalaprilat did not stimulate calcium signaling in HEK 293a cells that expressed B1Rs. A typical ACE inhibitor did not bind to nor stimulate the human B1Rs; nevertheless, several other indirect mechanisms could connect ACE inhibition to B1R stimulation in vivo.

Imidaprilat inhibits matrix metalloproteinase-2 activity in human cardiac fibroblasts induced by interleukin-1beta via NO-dependent pathway

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors are widely used in treatment of heart failure, but little is known regarding whether ACE inhibitors regulate the activity of matrix metalloproteinases (MMPs) and the tissue inhibitor of MMPs (TIMPs) in cardiac cells. The purpose of this study was to determine the ability and possible signal pathway involved of imidaprilat, an ACE inhibitor, to modulate MMP-2 and TIMP-2 in human cardiac fibroblasts in the presence of interleukin (IL)-1beta.

METHODS AND RESULTS

Using gelatin zymography and RT-PCR and Griess analysis,we found that IL-1beta increased the MMP-2 activity and transcription and nitric oxide(NO) production from supernatant of culture medium. These effects of IL-1beta were inhibited by imidaprilat or the NO synthase inhibitor, L-NMMA. Sodium nitroprusside (SNP), an exogenous NO donor, prevented significantly the effects of imidaprilat on MMP-2 inhibition. Imidaprilat alone didn't affect MMP-2 activity and expression. Neither IL-1beta nor imidaprilat has no effect on TIMP-2 transcription in cardiac fibroblasts.

CONCLUSIONS

The current study demonstrates imidaprilat inhibits MMP-2 activity and expression in human cardiac fibroblasts induced by IL-1beta via NO-dependent pathway. These data suggest that the beneficial effect of ACE inhibitors against left cardiac remodeling and heart failure may be due at least in part to regulating MMPs activity and expression by modulation of NO pathway.

Carboxypeptidase M and kinin B1 receptors interact to facilitate efficient b1 signaling from B2 agonists

Kinin B1 receptor (B1R) expression is induced by injury or inflammatory mediators, and its signaling produces both beneficial and deleterious effects. Kinins cleaved from kininogen are agonists of the B2R and must be processed by a carboxypeptidase to generate B1R agonists des-Arg(9)-bradykinin or des-Arg(10)-kallidin. Carboxypeptidase M (CPM) is a membrane protein potentially well suited for this function. Here we show that CPM expression is required to generate a B1R-dependent increase in [Ca(2+)](i) in cells stimulated with B2R agonists kallidin or bradykinin. CPM and the B1R interact on the cell membrane, as shown by co-immunoprecipitation, cross-linking, and fluorescence resonance energy transfer analysis. CPM and B1R are also co-localized in lipid raft/caveolin-enriched membrane fractions, as determined by gradient centrifugation. Treatment of cells co-expressing CPM and B1R with methyl-beta-cyclodextrin to disrupt lipid rafts reduced the B1R-dependent increase in [Ca(2+)](i) in response to B2R agonists, whereas cholesterol treatment enhanced the response. A monoclonal antibody to the C-terminal beta-sheet domain of CPM reduced the B1R response to B2R agonists without inhibiting CPM. Cells expressing a novel fusion protein containing CPM at the N terminus of the B1R also increased [Ca(2+)](i) when stimulated with B2R agonists, but the response was not reduced by methyl-beta-cyclodextrin or CPM antibody. A B1R- and CPM-dependent calcium signal in response to B2R agonist bradykinin was also found in endothelial cells that express both proteins. Thus, a close relationship of B1Rs and CPM on the membrane is required for efficiently generating B1R signals, which play important roles in inflammation.

Structure and function of human plasma carboxypeptidase N, the anaphylatoxin inactivator

Human carboxypeptidase N (CPN) was discovered in the early 1960s as a plasma enzyme that inactivates bradykinin and was identified 8 years later as the major "anaphylatoxin inactivator" of blood. CPN plays an important role in protecting the body from excessive buildup of potentially deleterious peptides that normally act as local autocrine or paracrine hormones. This review summarizes the structure, enzymatic properties and function of this important human enzyme, including insights gained by the recent elucidation of the crystal structure of the CPN catalytic subunit and structural modeling of the non-catalytic regulatory 83 kDa subunit. We also discuss its physiological role in cleaving substrates such as kinins, anaphylatoxins, creatine kinase, plasminogen receptors, hemoglobin and stromal cell-derived factor-1alpha (SDF-1alpha).

Human ACE and bradykinin B2 receptors form a complex at the plasma membrane

To investigate how angiotensin I-converting enzyme (ACE) inhibitors enhance the actions of bradykinin (BK) on B2 receptors independent of blocking BK inactivation, we expressed human somatic ACE and B2 receptors in CHO cells. Bradykinin and its ACE-resistant analog were the receptor agonists. B2 fused with green fluorescent protein (GFP) and ACE were coprecipitated with antisera to GFP or ACE shown in Western blots. Immunohistochemistry of fixed cells localized ACE by red color and B2-GFP by green. Yellow on plasma membranes of coexpressing cells also indicated enzyme-receptor complex formation. Using ACE-fused cyan fluorescent protein donor and B2-fused yellow fluorescent protein (YFP) acceptor, we registered fluorescence resonance energy transfer (FRET) by the enhanced fluorescence of donor on acceptor photobleaching, establishing close (within 10 nm) positions of B2 receptors and ACE. Bradykinin stimulation cointernalized ACE and B2 receptors. We expressed ACE fused to N terminus of B2 receptors, anchoring only receptors to plasma membranes. Here, in contrast to cells, where both ACE and B2 receptors are separately anchored, ACE inhibitors neither enhance activation of chimeric B2 nor resensitize desensitized B2 receptors. Heterodimer formation between ACE and B2 receptors can be a mechanism for ACE inhibitors to augment kinin activity at cellular level.

Fibroblast Growth Factor-2 Mediates Angiotensin-Converting Enzyme Inhibitor-Induced Angiogenesis in Coronary Endothelium

The beneficial effect exerted by angiotensin-converting enzyme inhibitors (ACEI) on vascular endothelium has been attributed to restoration of endothelial cell survival properties and improvement of angiogenesis. Fibroblast growth factor (FGF)-2 is an angiogenic factor for the microvascular endothelium, which tonically promotes endothelial cell growth and survival through an autocrine/paracrine mechanism. Here, we formulate the hypothesis that FGF-2 might contribute to the prosurvival/proangiogenic effect of ACEI. We investigated zofenoprilat and, in selected experiments, lisinopril, as representatives of ACEI. These compounds induced formation of pseudocapillaries in vessel fragments isolated from porcine coronary and human umbilical arteries by increasing endothelial cell growth up to 5-fold. Angiogenesis was abolished by inhibitors of nitric-oxide synthase (NOS) pathway and by anti-FGF-2 antibodies. Consistently, in cultured coronary endothelial cells (CVECs), ACEI up-regulated endothelial NOS (eNOS) and FGF-2 and induced mitogen-activated protein kinase extracellular signal-regulated kinase 1/2 activation. The overexpression of eNOS/FGF-2 produced, at the functional level, enhanced cell proliferation and migration, the latter effect being dose-dependent and maximal at 0.1 microM zofenoprilat. The importance of FGF-2 for the acquisition of the angiogenic phenotype elicited by ACEI was clearly demonstrated by the impairment of endothelial functions following transfection of CVECs with small interference RNA for FGF-2. Moreover, FGF-2 silencing greatly affected the nuclear translocation of the FGF receptor (FGFR)-1, highlighting the autocrine mode of action of FGF-2. At the endothelial membrane level, zofenoprilat appeared to activate the bradykinin B1 receptor, a known stimulant of FGF-2 expression. In conclusion, we show that ACEI exert protective/proangiogenic effects in microvascular coronary endothelial cells by activating the endogenous FGF-2/FGFR-1 system.