Altered cardiac endothelin receptors and protein kinase C in deoxycorticosterone-salt hypertensive rats

Protein Kinase C Inhibitors as Modulators of Vascular Function and their Application in Vascular Disease

Blood pressure (BP) is regulated by multiple neuronal, hormonal, renal and vascular control mechanisms. Changes in signaling mechanisms in the endothelium, vascular smooth muscle (VSM) and extracellular matrix cause alterations in vascular tone and blood vessel remodeling and may lead to persistent increases in vascular resistance and hypertension (HTN). In VSM, activation of surface receptors by vasoconstrictor stimuli causes an increase in intracellular free Ca(2+) concentration ([Ca(2+)]i), which forms a complex with calmodulin, activates myosin light chain (MLC) kinase and leads to MLC phosphorylation, actin-myosin interaction and VSM contraction. Vasoconstrictor agonists could also increase the production of diacylglycerol which activates protein kinase C (PKC). PKC is a family of Ca(2+)-dependent and Ca(2+)-independent isozymes that have different distributions in various blood vessels, and undergo translocation from the cytosol to the plasma membrane, cytoskeleton or the nucleus during cell activation. In VSM, PKC translocation to the cell surface may trigger a cascade of biochemical events leading to activation of mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK), a pathway that ultimately increases the myofilament force sensitivity to [Ca(2+)]i, and enhances actin-myosin interaction and VSM contraction. PKC translocation to the nucleus may induce transactivation of various genes and promote VSM growth and proliferation. PKC could also affect endothelium-derived relaxing and contracting factors as well as matrix metalloproteinase (MMPs) in the extracellular matrix further affecting vascular reactivity and remodeling. In addition to vasoactive factors, reactive oxygen species, inflammatory cytokines and other metabolic factors could affect PKC activity. Increased PKC expression and activity have been observed in vascular disease and in certain forms of experimental and human HTN. Targeting of vascular PKC using PKC inhibitors may function in concert with antioxidants, MMP inhibitors and cytokine antagonists to reduce VSM hyperactivity in certain forms of HTN that do not respond to Ca(2+) channel blockers.

Endothelin 1 activation of endothelin A receptor/NADPH oxidase pathway and diminished antioxidants critically contribute to endothelial progenitor cell reduction and dysfunction in salt-sensitive hypertension

Circulating endothelial progenitor cells (EPCs) are reduced in hypertension, which inversely correlates with its mortality. Deoxycorticosterone acetate (DOCA)-salt hypertension features elevated endothelin (ET) 1 and oxidative stress. We tested the hypothesis that ET-1 induces EPC dysfunction by elevating oxidative stress through the ET(A)/NADPH oxidase pathway in salt-sensitive hypertension. Both ET(A) and ET(B) receptors were expressed in EPCs, but only ET(A) receptors were significantly increased in EPCs of DOCA-salt rats. EPC number and function were reduced in DOCA-salt rats compared with sham controls, and both were reversed by in vivo blockade of ET(A) receptors or NADPH oxidase. The enzymatic activities of NAPDH oxidase and its subunits gp91(phox), p22(phox), and Rac1 were augmented in EPCs of DOCA-salt rats, with concomitantly decreased antioxidant enzymes manganese superoxide dismutase, copper-zinc superoxide dismutase, and glutathione peroxidase 1. Reactive oxygen species level was elevated in EPCs from DOCA-salt rats, accompanied by increased EPC telomerase inactivation, senescence, and apoptosis, which were rescued by ET(A) or NADPH oxidase blockade. Cell therapy of normal or treated DOCA EPCs, but not untreated DOCA EPCs, significantly increased capillary density and blood perfusion in ischemic hindlimbs of DOCA-salt rats. p53 and Bax/Bcl-2 ratios were increased in EPCs of DOCA-salt rats, which were reversed by ET(A) antagonist, NADPH oxidase inhibitor, or polyethylene glycol-superoxide dismutase. Finally, in ET(B)-deficient rats, plasma ET-1 was elevated, and EPC number and telomerase activity were diminished. These results demonstrate, for the first time, that both ET-1 activation of ET(A)/NADPH oxidase pathway and diminished antioxidants critically contribute to EPC reduction and dysfunction via increased oxidative stress in salt-sensitive hypertension.

Use of 2-aminoprop-1-ene-1,1,3-tricarbonitrile for the synthesis of tetrahydronaphthalene, hexahydroisoquinoline and hexahydrocinnoline derivatives with potential antitumor activities

The aim of the work was to synthesize heterocyclic compounds from 2-aminoprop-1-ene-1,1,3-tricarbonitrile and to study their antitumor activities. The title reagent reacted with cyclohexanone to give the ethylidene derivative 2. The reactivity of the latter product towards different chemical reagents was studied to give tetrahydronaphthalene, hexahydroisoquinoline and hexahydrocinnoline derivatives. The newly synthesized products were screened as antitumor agents on the in vitro growth of three human tumor cell lines representing different tumor types, namely, breast adenocarcinoma (MCF-7), non-small cell lung cancer (NCI-H460) and CNS cancer (SF-268). It was found that some of these compounds showed inhibitory effects on the three cell lines, indicating their potential use in the development of oncology products.

A pharmacological study on Berberis vulgaris fruit extract

Berberis vulgaris fruit (barberry) is known for its antiarrhythmic and sedative effects in Iranian traditional medicine. The effects of crude aqueous extract of barberry on rat arterial blood pressure and the contractile responses of isolated rat aortic rings and mesenteric bed to phenylephrine were investigated. We also examined effect of the extract on potassium currents recorded from cells in parabrachial nucleus and cerebellum rejoins of rat brain. Administration of the extract (0.05-1 mg/100 g body weight of rat) significantly reduced the mean arterial blood pressure and heart rate in anaesthetized normotensive and desoxycorticosteron acetate-induced hypertensive rats in a dose-dependent manner. Concentration-response curves for phenylephrine effects on isolated rat aortic rings and the isolated mesenteric beds in the presence of the extract were significantly shifted to the right. Application of the extract (1-50 microg/ml) shifted the activation threshold voltage to more negative potentials, leading to an enhancement in magnitude of the outward potassium current recorded from cells present in rat brain slices of parabrachial nucleus and cerebellum. This effect on potassium current may explain the sedative and neuroprotective effects of barberry. The present data support the hypothesis that the aqueous extract of barberry has beneficial effects on both cardiovascular and neural system suggesting a potential use for treatment of hypertension, tachycardia and some neuronal disorders, such as epilepsy and convulsion.

Protein kinase C isoforms as specific targets for modulation of vascular smooth muscle function in hypertension

Vascular contraction is an important determinant of the peripheral vascular resistance and blood pressure. The mechanisms underlying vascular smooth muscle (VSM) contraction and the pathological changes that occur in hypertension have been the subject of numerous studies and interpretations. Activation of VSM by vasoconstrictor stimuli at the cell surface causes an increase in [Ca(2+)](i), Ca(2+)-dependent activation of myosin light chain (MLC) kinase, MLC phosphorylation, actin-myosin interaction and VSM contraction. Additional signaling pathways involving Rho-kinase and protein kinase C (PKC) may increase the myofilament force sensitivity to [Ca(2+)](i) and MLC phosphorylation, and thereby maintain vascular contraction. PKC is a particularly intriguing protein kinase as it comprises a family of Ca(2+)-dependent and Ca(2+)-independent isoforms, which have different tissue and subcellular distribution, and undergo differential translocation during cell activation. PKC translocation to the cell surface may trigger a cascade of protein kinases, such as mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK) that ultimately interact with the contractile myofilaments and cause VSM contraction. Also, PKC translocation to the nucleus may promote VSM growth and proliferation. Increased PKC expression and activity have been identified in several forms of hypertension. The subcellular location of PKC may determine the state of VSM activity, and may be useful in the diagnosis/prognosis of hypertension. Vascular PKC isoforms may represent specific targets for modulation of VSM hyperactivity, and isoform-specific PKC inhibitors may be useful in treatment of Ca(2+) antagonist-resistant forms of hypertension.

Enhanced expression of fibrillin-1, a constituent of the myocardial extracellular matrix in fibrosis

Fibrillin-1 localization in the myocardium and the modulation of its expression in cardiac fibrosis were examined. In normal rat hearts, fibrillin-1 was abundant throughout the myocardium as thin fibers that crossed over the perimysium and around arteries. After cardiac fibrosis was induced in rats by either 14-day ANG II infusion or 21-day DOCA-salt treatment [a high endothelin-1 (ET-1) model], fibrillin-1 immunostaining was stronger in the interstitium (2.8-fold and 4.4-fold increases, respectively, in each model), extended between myocytes, and accumulated in microscopic scars and in the perivascular area of both ventricles. mRNA analysis confirmed its enhanced ventricular expression in both groups of rats (2.5-fold and 6.6-fold increments, respectively, in each model). In 1B normotensive and 2C hypertensive transgenic mice, two lines expressing an ANG II fusion protein in cardiac myocytes, strong fibrillin-1 immunoreactivity was observed in the interstitium and around arteries (3.7-fold and 7-fold increases, respectively). ANG II and transforming growth factor-beta1 enhanced fibrillin-1 synthesis by cardiac fibroblasts. Some fibrillin-1 fragments interacted with RGD-dependent integrins, including alpha(8)beta(1)-integrin, of cardiac fibroblasts but not necessarily through the RGD motif. Our findings illustrate that fibrillin-1 is an important constituent of the myocardium. In vitro and in vivo evidence suggests that ANG II can directly induce fibrillin-1 expression in cardiac fibroblasts. This protein can thus contribute to reactive and reparative processes.

Endothelin-1 is an essential co-factor for beta2-adrenergic receptor-induced proliferation of human cardiac fibroblasts

We previously demonstrated that chronic stimulation of the beta2-adrenergic receptor (beta2-AR) increases proliferation of cultured human cardiac fibroblasts (CF) via an autocrine mechanism. Here, we investigated the role of endothelin-1 (ET-1) in this process. ETA-receptor antagonism or protein kinase C inhibition abolished the beta2-AR-induced increase in cell proliferation. RT-PCR and ELISA analysis demonstrated that although CF synthesized and secreted ET-1, this occurred independently of beta2-AR stimulation. Furthermore, despite activation of the MAP kinase pathway, ET-1 treatment did not stimulate CF proliferation. Therefore, the role of ET-1 in this process is that of an essential co-factor acting independently of beta2-AR stimulation.

Endothelial dysfunction in aortic rings and mesenteric beds isolated from deoxycorticosterone acetate hypertensive rats: possible involvement of protein kinase C

The main objectives of this study were to investigate the effects of deoxycorticosterone acetate (DOCA)-induced hypertension on the aortic and mesenteric vascular responses to vasodilator and vasoconstrictor agents and also to elucidate whether protein kinase C (PKC) was involved in these responses, by using chelerythrine and calphostin C, the inhibitors of protein kinase C. Hypertension was induced in male Sprague-Dawley rats (200-250 g) by DOCA-salt injection [20 mg/kg, twice weekly for 5 weeks, subcutaneously (s.c.)] and NaCl (1%) was added to their drinking water. Control rats received a saline injection (0.5 ml/kg, twice weekly for 5 weeks, s.c.), then the animals were anaesthetised [thiopental, 30 mg/kg, intraperitoneally (i.p.)] and the arterial blood pressure was measured. Mean arterial blood pressure in control and hypertensive rats were 98+/-7.5 and 163+/-3.5 mmHg, respectively (P<0.0001). In the in vitro studies, rings of descending aorta and mesenteric beds were precontracted with phenylephrine and then concentration-response curves to acetylcholine and sodium nitroprusside were constructed. In the tissue removed from hypertensive rats, the responses to acetylcholine, but not to sodium nitroprusside, were significantly reduced. However, addition of chelerythrine (10 microM) or calphostin C (100 nM) to the organ bath significantly restored these impaired responses. Our data suggest that protein kinase C plays a crucial role in the endothelial dysfunction induced by hypertension.

Both endothelin-A and endothelin-B receptors are present on adult rat cardiac ventricular myocytes

Endothelin-A (ET(A)) and endothelin-B (ET(B)) receptors have been demonstrated in intact heart and cardiac membranes. ET(A) receptors have been demonstrated on adult ventricular myocytes. The aim of the present study was to determine the presence of ET(B) and the relative contribution of this receptor subtype to total endothelin-1 (ET-1) binding on adult ventricular myocytes. Saturation binding experiments indicated that ET-1 bound to a single population of receptors (Kd = 0.52 +/- 0.13 nM, n = 4) with an apparent maximum binding (Bmax) of 2.10 +/- 0.25 sites (x 10(5))/cell (n = 4). Competition experiments using 40 pM [125I]ET-1 and nonradioactive ET-1 revealed a Ki of 660 +/- 71 pM (n = 10) and a Hill coefficient (nH) of 0.99 +/- 0.10 (n = 10). A selective ET(A) antagonist, BQ610, displaced 80% of the bound [125I]ET-1. No displacement was observed by concentrations of an ET(B)-selective antagonist, BQ788, up to 1.0 microM. However, in the presence of 1.0 microM BQ610, BQ788 inhibited the remaining [125I]ET-1 binding. Similarly, in the presence of 1.0 microM BQ788, BQ610 inhibited the remaining specific [125I]ET-1 binding. Binding of an ET(B1)-selective agonist, [125I]IRL-1620, confirmed the presence of ET(B). ET(B) bound to ET-1 irreversibly, whereas binding to ET(A) demonstrated both reversible and irreversible components, and BQ610 and BQ788 bound reversibly. Reducing the incubation temperature to 0 degrees C did not alter the irreversible component of ET-1 binding. Hence, both ET(A) and ET(B) receptors are present on intact adult rat ventricular myocytes, and the ratio of ET(A):ET(B) binding sites is 4:1. Both receptor subtypes bind to ET-1 by a two-step association involving the formation of a tight receptor-ligand complex; however, the kinetics of ET-1 binding to ET(A) versus ET(B) differ.

Arrhythmogenic and inotropic effects of interferon investigated in perfused and in vivo rat hearts: influences of cardiac hypertrophy and isoproterenol

Although the arrhythmogenic effects of interferon (IF) have been reported in clinical practice, the experimental data are limited. Therefore, these effects were investigated in in vivo and Langendorff-perfusion studies using 3 different groups of rats (ie, control, aorta-banded, and deoxycorticosterone acetate (DOCA)-salt hypertension groups) in the presence or absence of isoproterenol. In the perfusion study, human recombinant IF-alpha (< or =15,000 U/ml) alone induced irreversible atrioventricular blockade in all groups, whereas this agent (< or =1,500 U/ml) caused negative inotropism and ventricular tachyarrhythmias (arrhythmic score greater in the order of DOCA-salt>aorta-banded = control group) in the preparations pretreated with isoproterenol (10(-9) mol/L). In an in vivo study, IF-alpha (6x10(6) U/kg) resulted in ventricular tachyarrhythmias only in the presence of isoproterenol (10 mg/kg), as in the perfusion study (arrhythmic score; DOCA-salt>aorta-banded>control). In conclusion, the arrhythmogenesis of IF-alpha is potentiated in pathophysiological conditions such as cardiac hypertrophy or elevated sympathetic activity.

Gender differences in vascular expression of endothelin and ET(A)/ET(B) receptors, but not in calcium handling mechanisms, in deoxycorticosterone acetate-salt hypertension

We determined if the increased vascular responsiveness to endothelin-1 (ET-1) observed in male, but not in female, DOCA-salt rats is associated with differential vascular mRNA expression of ET-1 and/or ET A/ET B receptors or with functional differences in Ca2+ handling mechanisms by vascular myocytes. Uninephrectomized male and female Wistar rats received DOCA and drinking water containing NaCl/KCl. Control rats received vehicle and tap water. Blood pressure and contractile responses of endothelium-denuded aortic rings to agents which induce Ca2+ influx and/or its release from internal stores were measured using standard procedures. Expression of mRNA for ET-1 and ET A/ET B receptors was evaluated by RT-PCR after isolation of total cell RNA from both aorta and mesenteric arteries. Systolic blood pressure was higher in male than in female DOCA rats. Contractions induced by Bay K8644 (which activates Ca2+ influx through voltage-operated L-type channels), and by caffeine, serotonin or ET-1 in Ca2+-free buffer (which reflect Ca2+ release from internal stores) were significantly increased in aortas from male and female DOCA-salt compared to control aortas. DOCA-salt treatment of male, but not female, rats statistically increased vascular mRNA expression of ET-1 and ET B receptors, but decreased the expression of ET A receptors. Molecular up-regulation of vascular ET B receptors, rather than differential changes in smooth muscle Ca2+ handling mechanisms, seems to account for the increased vascular reactivity to ET-1/ET B receptor agonists and higher blood pressure levels observed in male DOCA-salt rats.

Altered PYK2 phosphorylation by ANG II in hypertensive vascular smooth muscle

Vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit increased cell growth compared with normotensive Wistar-Kyoto rats (WKY). ANG II stimulates growth via G(q)-protein-coupled signaling that involves changes in cytosolic intracellular Ca(2+) concentration ([Ca(2+)](i)) and activation of protein kinase C (PKC) and mitogen-activated protein kinases. This study examines the role of the proline-rich tyrosine kinase 2 (PYK2) in hypertensive VSMC. Basal PYK2 phosphorylation in SHR VSMC was increased compared with WKY (0.44 +/- 0.02 vs. 0.20 +/- 0.02-fold). ANG II-induced activation of PYK2 in SHR VSMC was of greater magnitude (2.2 +/- 0.2-fold in SHR; 1.4 +/- 0.1-fold in WKY) and occurred more rapidly (peak activation at 2 min in SHR vs. 5 min in WKY). This effect was blocked by pretreatment with the [Ca(2+)](i) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or the PKC inhibitor chelerythrine. Basal and ANG II-stimulated c-Fos expression was increased in SHR versus WKY VSMC. PYK2 downregulation with antisense oligonucleotides blocked ANG II-induced c-Fos expression. Increased PYK2 activation may be altered signaling cascades that regulate cell growth in hypertensive VSMC.