The bradykinin B1 receptor and the central regulation of blood pressure in spontaneously hypertensive rats

Bradykinin 1 receptor blockade subdues systemic autoimmunity, renal inflammation, and blood pressure in murine lupus nephritis

OBJECTIVE

The goal of this study was to explore the role of bradykinins and bradykinin 1 receptor (B1R) in murine lupus nephritis.

METHODS

C57BL/6 and MRL/lpr mice were compared for renal expression of B1R and B2R by western blot and immunohistochemistry. MRL/lpr lupus-prone mice were administered the B1R antagonist, SSR240612 for 12 weeks, and monitored for blood pressure, proteinuria, renal function, and serum autoantibodies.

RESULTS

Renal B1R:B2R ratios were significantly upregulated in MRL/lpr mice compared with B6 controls. B1R blockade ameliorated renal pathology lesions, proteinuria, and blood pressure, accompanied by lower serum IgG and anti-dsDNA autoantibody levels, reduced splenic marginal zone B cells and CD4⁺ T cells, and renal infiltrating CD4⁺ T cells, macrophages, and neutrophils. Both urine and renal CCL2 and CCL5 chemokines were also decreased in the B1R blocked MRL/lpr mice.

CONCLUSION

Bradykinin receptor B1R blockade ameliorates both systemic immunity and renal inflammation possibly by inhibiting multiple chemokines and renal immune cell infiltration. B1R blockade may be particularly attractive in subjects with concomitant lupus nephritis and hypertension.

Kinin B1 Receptor Promotes Neurogenic Hypertension Through Activation of Centrally Mediated Mechanisms

Hypertension is associated with increased activity of the kallikrein-kinin system. Kinin B1 receptor (B1R) activation leads to vasoconstriction and inflammation. Despite evidence supporting a role for the B1R in blood pressure regulation, the mechanisms by which B1R could alter autonomic function and participate in the pathogenesis of hypertension remain unidentified. We sought to explore whether B1R-mediated inflammation contributes to hypertension and investigate the molecular mechanisms involved. In this study, we tested the hypothesis that activation of B1R in the brain is involved in the pathogenesis of hypertension, using the deoxycorticosterone acetate-salt model of neurogenic hypertension in wild-type and B1R knockout mice. Deoxycorticosterone acetate-salt treatment in wild-type mice led to significant increases in B1R mRNA and protein levels and bradykinin levels, enhanced gene expression of carboxypeptidase N supporting an increase in the B1R ligand, associated with enhanced blood pressure, inflammation, sympathoexcitation, autonomic dysfunction, and impaired baroreflex sensitivity, whereas these changes were blunted or prevented in B1R knockout mice. B1R stimulation was further shown to involve activation of the ASK1-JNK-ERK1/2 and NF-κB pathways in the brain. To dismiss potential developmental alterations in knockout mice, we further used B1R blockade selectively in the brain of wild-type mice. Supporting the central origin of this mechanism, intracerebroventricular infusion of a specific B1R antagonist, attenuated the deoxycorticosterone acetate-salt-induced increase in blood pressure in wild-type mice. Our data provide the first evidence of a central role for B1R-mediated inflammatory pathways in the pathogenesis of deoxycorticosterone acetate-salt hypertension and offer novel insights into possible B1R-targeted therapies for the treatment of neurogenic hypertension.

Excess of Aminopeptidase A in the Brain Elevates Blood Pressure via the Angiotensin II Type 1 and Bradykinin B2 Receptors without Dipsogenic Effect

Aminopeptidase A (APA) cleaves angiotensin (Ang) II, kallidin, and other related peptides. In the brain, it activates the renin angiotensin system and causes hypertension. Limited data are available on the dipsogenic effect of APA and pressor effect of degraded peptides of APA such as bradykinin. Wistar-Kyoto rats received intracerebroventricular (icv) APA in a conscious, unrestrained state after pretreatment with (i) vehicle, (ii) 80 μg of telmisartan, an Ang II type-1 (AT1) receptor blocker, (iii) 800 nmol of amastatin, an aminopeptidase inhibitor, and (iv) 1 nmol of HOE-140, a bradykinin B2 receptor blocker. Icv administration of 400 and 800 ng of APA increased blood pressure by 12.6 ± 3.0 and 19.0 ± 3.1 mmHg, respectively. APA did not evoke drinking behavior. Pressor response to APA was attenuated on pretreatment with telmisartan (vehicle: 22.1 ± 2.2 mmHg versus telmisartan: 10.4 ± 3.2 mmHg). Pressor response to APA was also attenuated with amastatin and HOE-140 (vehicle: 26.5 ± 1.1 mmHg, amastatin: 14.4 ± 4.2 mmHg, HOE-140: 16.4 ± 2.2 mmHg). In conclusion, APA increase in the brain evokes a pressor response via enzymatic activity without dipsogenic effect. AT1 receptors and B2 receptors in the brain may contribute to the APA-induced pressor response.

An interaction of renin-angiotensin and kallikrein-kinin systems contributes to vascular hypertrophy in angiotensin II-induced hypertension: in vivo and in vitro studies

The kallikrein-kinin and renin-angiotensin systems interact at multiple levels. In the present study, we tested the hypothesis that the B1 kinin receptor (B1R) contributes to vascular hypertrophy in angiotensin II (ANG II)-induced hypertension, through a mechanism involving reactive oxygen species (ROS) generation and extracellular signal-regulated kinase (ERK1/2) activation. Male Wistar rats were infused with vehicle (control rats), 400 ng/Kg/min ANG II (ANG II rats) or 400 ng/Kg/min ANG II plus B1 receptor antagonist, 350 ng/Kg/min des-Arg(9)-Leu(8)-bradykinin (ANGII+DAL rats), via osmotic mini-pumps (14 days) or received ANG II plus losartan (10 mg/Kg, 14 days, gavage - ANG II+LOS rats). After 14 days, ANG II rats exhibited increased systolic arterial pressure [(mmHg) 184 ± 5.9 vs 115 ± 2.3], aortic hypertrophy; increased ROS generation [2-hydroxyethidium/dihydroethidium (EOH/DHE): 21.8 ± 2.7 vs 6.0 ± 1.8] and ERK1/2 phosphorylation (% of control: 218.3 ± 29.4 vs 100 ± 0.25]. B1R expression was increased in aortas from ANG II and ANG II+DAL rats than in aortas from the ANG II+LOS and control groups. B1R antagonism reduced aorta hypertrophy, prevented ROS generation (EOH/DHE: 9.17 ± 3.1) and ERK1/2 phosphorylation (137 ± 20.7%) in ANG II rats. Cultured aortic vascular smooth muscle cells (VSMC) stimulated with low concentrations (0.1 nM) of ANG II plus B1R agonist exhibited increased ROS generation, ERK1/2 phosphorylation, proliferating-cell nuclear antigen expression and [H3]leucine incorporation. At this concentration, neither ANG II nor the B1R agonist produced any effects when tested individually. The ANG II/B1R agonist synergism was inhibited by losartan (AT1 blocker, 10 µM), B1R antagonist (10 µM) and Tiron (superoxide anion scavenger, 10 mM). These data suggest that B1R activation contributes to ANG II-induced aortic hypertrophy. This is associated with activation of redox-regulated ERK1/2 pathway that controls aortic smooth muscle cells growth. Our findings highlight an important cross-talk between the DABK and ANG II in the vascular system and contribute to a better understanding of the mechanisms involved in vascular remodeling in hypertension.

Blood borne hormones in a cross-talk between peripheral and brain mechanisms regulating blood pressure, the role of circumventricular organs

Accumulating evidence suggests that blood borne hormones modulate brain mechanisms regulating blood pressure. This appears to be mediated by the circumventricular organs which are located in the walls of the brain ventricular system and lack the blood-brain barrier. Recent evidence shows that neurons of the circumventricular organs express receptors for the majority of cardiovascular hormones. Intracerebroventricular infusions of hormones and their antagonists is one approach to evaluate the influence of blood borne hormones on the neural mechanisms regulating arterial blood pressure. Interestingly, there is no clear correlation between peripheral and central effects of cardiovascular hormones. For example, angiotensin II increases blood pressure acting peripherally and centrally, whereas peripherally acting pressor catecholamines decrease blood pressure when infused intracerebroventricularly. The physiological role of such dual hemodynamic responses has not yet been clarified. In the paper we review studies on hemodynamic effects of catecholamines, neuropeptide Y, angiotensin II, aldosterone, natriuretic peptides, endothelins, histamine and bradykinin in the context of their role in a cross-talk between peripheral and brain mechanisms involved in the regulation of arterial blood pressure.

Contribution of the central dopaminergic system in the anti-hypertensive effect of kinin B1 receptor antagonists in two rat models of hypertension

Kinins are neuroactive peptides that could play a role in central autonomic control of blood pressure. Whereas kinin B1R binding sites were increased in specific brain areas of spontaneously hypertensive rats (SHR) and Angiotensin II (AngII)-hypertensive rats, the contribution of kinin B1R in hypertension remains controversial. The aims of the study were to determine: (a) the effects on mean arterial blood pressure (MAP) of centrally and peripherally administered B1R antagonists in SHR (16weeks) and AngII-hypertensive rats (200ng/kg/minx2weeks, s.c.); (b) the contribution of central dopamine in the effects of SSR240612. The rationale is based on the overactivity of the dopaminergic system in hypertension. In both models, SSR240612 (1, 5 and 10mg/kg, gavage) reduced dose-dependently MAP (-75mm Hg at least up to 6-8h) and this therapeutic effect was resolved after 24h. At the dose of 5mg/kg, SSR240612-induced anti-hypertension was prevented by two dopamine receptor blockers, namely raclopride (0.16mg/kg, i.v.) and haloperidol (10mg/kg, s.c.). I.c.v. SSR240612 (1mug) decreased rapidly MAP in both models (1-6h) via a raclopride sensitive mechanism. In comparison, peripherally acting B1R antagonists (R-715 and R-954, 2mg/kg, s.c.) caused shorter and very modest decreases of MAP (from -20 to -30mm Hg). Centrally or peripherally administered B1R antagonists had no effect on MAP in control Wistar-Kyoto rats. Data provide the first pharmacological evidence that the up-regulated brain kinin B1R contributes through a central dopaminergic mechanism (DA-D2R) to the maintenance of arterial hypertension in genetic and experimental animal models of hypertension.

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

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

CGS 35601, a Triple Inhibitor of Angiotensin Converting Enzyme, Neutral Endopeptidase and Endothelin Converting Enzyme

CGS 35601 (L-tryptophan, N-[[1-[[(2S)-2-mercapto-4-methyl-1-oxopentyl]amino]-cyclopentyl]carbonyl]) is one of a few single molecules capable of inhibiting the activities of angiotensin-converting enzyme (ACE), neutral endopeptidase (NEP) and endothelin converting enzyme (ECE) simultaneously, with IC(50) values of 22, 2, and 55 nM, respectively. Through the inhibition of ACE and ECE, it blocks the conversion of angiotensin I (AI) and big endothelin-1 (big ET-1) into the two most potent peptidic vasoconstrictors, angiotensin II (AII) and ET-1, respectively. By inhibiting NEP, CGS 35601 also prevents the degradation of peptidic vasodilators such as bradykinin (BK), natriuretic peptides (NPs) and adrenomedullin (ADM) and, hence, modulates the secondary release of other vasoactive mediators such as nitric oxide (NO) and prostaglandins. In chronic (30 days) experiments, CGS 35601 is well tolerated with a very good safety profile in healthy normotensive, hypertensive and type 2 diabetic rats. The antihypertensive efficacy of CGS 35601 was demonstrated in chronically instrumented, unrestrained and conscious rat models of hypertension (SHR and DSS) and type 2 diabetes (ZDF-fatty). It lowered blood pressure effectively as well as modulated plasma concentrations of a number of circulating vasoactive peptidic mediators that are keys to the regulation of the vascular tone. These data suggest that CGS 35601, a triple vasopeptidase inhibitor (VPI), may represent a novel class of antihypertensive drugs and may have the potential to reduce morbidity and mortality from cardiovascular disorders, diabetes and subsequent renal complications. Similar in vivo ACE, NEP, and ECE inhibitory activities were also observed with the orally active prodrug, CGS 37808 (L-tryptophan, N-[[1-[[(2S)-2-(acetylthio)-4-methyl-1-oxopentyl]amino]cyclopentyl]-carbonyl]-, methyl ester.

Effects of alpha-lipoic acid on kinin B1 and B2 receptor binding sites in the spinal cord of chronically angiotensin-treated rats

A quantitative autoradiographic study was performed to determine whether kinin receptors are altered in the rat spinal cord in an experimental model of arterial hypertension under antioxidant therapy with alpha-lipoic acid. Sprague-Dawley rats were fed for 4 weeks with a normal chow diet or with an alpha-lipoic acid supplemented diet (1000 mg/kg feed), and treated for the last 2 weeks with angiotensin II (AT II) (200 ng/kg/min with an osmotic pump implanted s.c.). Control rats received either diet but not AT II. A 2-week administration of AT II increased significantly systolic blood pressure, the production of superoxide anion in the aorta and B1 receptor binding sites in the thoracic spinal dorsal horn. This treatment did not affect spinal B2 receptor binding sites, glycemia and insulinemia. The diet supplemented with alpha-lipoic acid reduced significantly the increase in systolic blood pressure, the production of aortic superoxide anion and prevented the increases of B1 receptor binding sites. Results show an association between the oxidative stress and the increases of B1 receptors and arterial blood pressure induced by AT II. Data also exclude the possibility that arterial hypertension is a primary mechanism leading to an increase of B2 receptor binding sites in the rat spinal cord.

International union of pharmacology. XLV. Classification of the kinin receptor family: from molecular mechanisms to pathophysiological consequences

Kinins are proinflammatory peptides that mediate numerous vascular and pain responses to tissue injury. Two pharmacologically distinct kinin receptor subtypes have been identified and characterized for these peptides, which are named B1 and B2 and belong to the rhodopsin family of G protein-coupled receptors. The B2 receptor mediates the action of bradykinin (BK) and lysyl-bradykinin (Lys-BK), the first set of bioactive kinins formed in response to injury from kininogen precursors through the actions of plasma and tissue kallikreins, whereas the B(1) receptor mediates the action of des-Arg9-BK and Lys-des-Arg9-BK, the second set of bioactive kinins formed through the actions of carboxypeptidases on BK and Lys-BK, respectively. The B2 receptor is ubiquitous and constitutively expressed, whereas the B1 receptor is expressed at a very low level in healthy tissues but induced following injury by various proinflammatory cytokines such as interleukin-1beta. Both receptors act through G alpha(q) to stimulate phospholipase C beta followed by phosphoinositide hydrolysis and intracellular free Ca2+ mobilization and through G alpha(i) to inhibit adenylate cyclase and stimulate the mitogen-activated protein kinase pathways. The use of mice lacking each receptor gene and various specific peptidic and nonpeptidic antagonists have implicated both B1 and B2 receptors as potential therapeutic targets in several pathophysiological events related to inflammation such as pain, sepsis, allergic asthma, rhinitis, and edema, as well as diabetes and cancer. This review is a comprehensive presentation of our current understanding of these receptors in terms of molecular and cell biology, physiology, pharmacology, and involvement in human disease and drug development.

Age-related changes of bradykinin B1 and B2 receptors in rat heart

Aging is a major risk factor for the development of vascular diseases, such as hypertension and atherosclerosis, that leads to end organ damage and especially heart failure. Bradykinin has been demonstrated to have a cardioprotective role by affecting metabolic processes and tissue perfusion under conditions of myocardial ischemia. Its actions are exerted via the bradykinin B1- and B2-type receptors (B1Rs and B2Rs), but the functional status of these receptors during the aging process is poorly understood. This study aims to investigate whether changes in B1R and B2R gene and protein expression in rat heart are associated with the age-related alterations of cardiac structure and function. Using real-time PCR, we found that B1R mRNA expression increased 2.9-fold in hearts of older rats (24 mo of age) compared with younger rats (3 mo of age), whereas B2R gene expression remained unchanged. Western blot analysis showed that expression of B2R at the protein level is approximately twofold higher in young rats compared with old rats, whereas the B1R protein is approximately twofold higher in old rats compared with young rats. The present results provide clear functional and molecular evidence that indicate age-related changes of bradykinin B1Rs and B2Rs in heart. Because the cardioprotective actions of bradykinin are physiologically mediated via the B2Rs, whereas the B1Rs become induced by tissue damage, these results suggest that age-related decreases in B2R protein levels may leave the heart vulnerable to ischemic damage, and increases in B1R expression and activity may represent a compensatory reaction in aging hearts.

Role of the B1 kinin receptor in the regulation of cardiac function and remodeling after myocardial infarction

Kinins exert cardioprotective effects via 2 G-protein-coupled receptors, B1 and B2. Using B1 kinin receptor gene knockout mice (B1-/-), we tested the hypotheses that the B1 receptor plays an important role in preservation of cardiac function, whereas lack of B1 may accelerate cardiac remodeling and dysfunction after myocardial infarction, and that B2 receptors may compensate for lack of B1, whereas blockade of B2 receptors in B1-/- mice may cause further deterioration of cardiac function and remodeling. Female B1-/- mice and wild-type controls (C57BL/6J, B1+/+) underwent sham surgery or myocardial infarction and were treated with either vehicle or B2-antagonist (icatibant, 500 microg/kg per day, subcutaneous) for 8 weeks. We found that in sham myocardial infarction, B1-/- mice had a larger left ventricular diastolic chamber dimension both initially and at 4 to 8 weeks compared with B1+/+. Left ventricular mass and myocyte size were also larger in B1-/- with sham operation than in B1+/+, although cardiac function did not differ between strains. After myocardial infarction, cardiac remodeling and function were similar in both strains, although B1-/- mice tended to have lower blood pressure. Blockade of B2 receptors tended to worsen cardiac remodeling and dysfunction in B1-/- but not in B1+/+. These results may suggest that B2 receptors play an important role in compensating for lack of B1 receptors in mice with myocardial infarction. Dual blockade of both B1 and B2 eliminates this compensation, leading to further deterioration of cardiac dysfunction and remodeling after myocardial infarction.

Renal protective role of bradykinin B1 receptor in stroke-prone spontaneously hypertensive rats

The kallikrein-kinin system plays important roles in blood pressure regulation, metabolism of electrolytes and organ protection. Although the bradykinin B2 receptor (B2R) has been reported to be involved in most of these effects, a role of the bradykinin B1 receptor (B1R) has also been noted recently. The aim of this study was to determine the role of renal B1R in stroke-prone spontaneously hypertensive rats (SHR-SP). Sixteen-week-old SHR-SP and Wistar Kyoto rats (WKY) as a control were used in the experiments. A high level of B1R mRNA was detected in SHR-SP, while the expression in WKY was almost undetectable. Immunohistochemistry revealed a B1R protein in the renal tubules and glomeruli in SHR-SP. The acute injection of a B1 R agonist into SHR-SP increased urinary NOx excretion to a level up to 5-fold higher than that in the SHR-SP treated with vehicle. The infusion of B1 R antagonist for 4 weeks resulted in a significant elevation of blood pressure and urinary albumin excretion and a decrease in urinary NOx excretion in SHR-SP. The administration of B1 R antagonist resulted in renal interstitial and glomerular fibrosis in SHR-SP. Moreover, the expressions of transforming growth factor (TGF) beta1 protein and collagen III mRNA in SHR-SP treated with B1R antagonist were significantly higher than those of SHR-SP treated with a vehicle. The expression and phosphorylation of extracellular signal-regulated protein kinase (ERK) and p38, but not c-Jun N-terminal kinase (JNK), were significantly increased in the SHR-SP treated with B1R antagonist. These results indicated that renal B1R might be over-expressed in a high blood pressure condition, and that this upregulated B1 R may play an important role in renal protection by inhibiting renal fibrosis via an increase of NO production and a suppression of TGFbeta1 expression and mitogen-activated protein kinase (ERK and p38) phosphorylation.

Correlation between brain bradykinin receptor binding sites and cardiovascular function in young and adult spontaneously hypertensive rats

Intracerebroventricular (i.c.v.) effects of bradykinin (BK) B(1) and B(2) receptor agonists and antagonists were assessed on mean arterial blood pressure (MAP) and heart rate (HR) in awake unrestrained spontaneously hypertensive rats (SHR, aged of 8 and 16 weeks) and age-matched Wistar Kyoto rats (WKY). Quantitative in vitro autoradiographic studies were also performed on the brain of both strains with specific radioligands for B(2) receptors [(125)I]HPP-Hoe 140 and B(1) receptors [(125)I]HPP-des-Arg(10) and Hoe140. MAP increased linearly with doses of BK (81-8100 pmol) and the amplitudes were significantly greater in SHR, particularly at 16 weeks. While BK evoked a negative linear trend on HR (bradycardia) in WKY, a positive one (tachycardia) was observed in adult SHR. In both strains, BK-induced pressor response was blocked by equimolar doses of B(2) receptor antagonist, D-Arg-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-BK (Hoe 140), but not by B(1) receptor antagonist, AcLys[D-betaNal(7), Ile(8)]des-Arg(9)-BK (R-715). B(1) receptor agonists (Sar-[D-Phe(8)]-des-Arg(9)-BK, des-Arg(9)-BK, des-Arg(10)-Kallidin) and antagonist (R-715 alone or with Hoe 140) had no or marginal effect on MAP and HR at doses up to 8100 pmol in SHR and WKY. Higher densities of specific [(125)I]HPP-Hoe 140 labelling were found in discrete brain areas of SHR, especially in regions associated with cardiovascular function. Low levels of [(125)I]HPP-[des-Arg(10)]-Hoe140 binding sites were seen in WKY and SHR, yet densities were significantly greater in midbrain and cortical regions of SHR aged of 16 weeks. Contrary to SHR, ageing caused a downregulation of B(2) and B(1) receptor binding sites in specific brain nuclei in WKY. It is concluded that the hypersensitivity of the pressor response to i.c.v. BK in SHR occurs during both the early and established phases of hypertension in parallel with the enhancement of B(2) receptor binding sites in various cardiovascular brain centres. In contrast, brain B(1) receptors do not seem to participate in the central pressor effects of kinins nor in the maintenance of hypertension in SHR.

Kinin B2 receptor is not involved in enalapril-induced apoptosis and regression of hypertrophy in spontaneously hypertensive rat aorta: possible role of B1 receptor

1. Treatment with enalapril induces smooth muscle cell apoptosis and regression of aortic hypertrophy in spontaneously hypertensive rats (SHRs), whereas combined blockade of angiotensin II AT(1) and AT(2) receptors does not. We postulated that vascular apoptosis with enalapril involves enhanced half-life of bradykinin (BK) and kinin B(2) receptor stimulation. 2. SHR, 11-weeks old, were treated for 4 weeks with enalapril (30 mg kg(-1) day(-1)), Hoe 140 (500 microg kg(-1) day(-1); B(2) receptor antagonist), alone or in combination. Controls received vehicle. 3. The half-life of hypotensive responses to intra-arterial bolus injections of BK were significantly increased in SHR anesthetized after 4 weeks of enalapril, an effect prevented by Hoe 140. The magnitude of BK-induced hypotension was significantly attenuated in all rats treated with Hoe 140. 4. As compared to placebo, enalapril treatment significantly reduced blood pressure (-34+/-2%), aortic hypertrophy (-20+/-3%), hyperplasia (-37+/-5%) and DNA synthesis (-61+/-8%), while it increased aortic DNA fragmentation by two-fold. Hoe 140 given alone or in combination with enalapril affected none of these parameters. 5. As a possible alternative mechanism, aortae isolated during the second week of enalapril treatment showed a transient upregulation of contractile responses to des-Arg(9)BK (EC(50)<1 nM), which were significantly reduced by [Leu(8)]des-Arg(9)BK (10 microM). Moreover, in vitro receptor autoradiography revealed an increase in expression of B(1) and B(2) receptor binding sites by 8-11 days of enalapril treatment. 6. Aortic apoptosis induction and hypertrophy regression with enalapril do not involve kinin B(2) receptors in SHR. Kinins acting via B(1) receptors remains a candidate mechanism.

Ten years of antisense inhibition of brain G-protein-coupled receptor function

Antisense oligonucleotides (AOs) are widely used as tools for inhibiting gene expression in the mammalian central nervous system. Successful gene suppression has been reported for different targets such as neurotransmitter receptors, neuropeptides, ion channels, trophic factors, cytokines, transporters, and others. This illustrates their potential for studying the expression and function of a wide range of proteins. AOs may even find therapeutic applications and provide an attractive strategy for intervention in diseases of the central nervous system (CNS). However, a lack of effectiveness and/or specificity could be a major drawback for research or clinical applications. Here we provide a critical overview of the literature from the past decade on AOs for the study of G-protein-coupled receptors (GPCRs). The following aspects will be considered: mechanisms by which AOs exert their effects, types of animal model system used, detection of antisense action, effects of AO design and delivery characteristics, non-antisense effects and toxicological properties, controls used in antisense studies to assess specificity, and our results (failures and successes). Although the start codon of the mRNA is the most popular region (46%) to target by AOs, targeting the coding region of GPCRs is almost as common (41%). Moreover, AOs directed to the coding region of the GPCR mRNA induce the highest reductions in receptor levels. To resist degradation by nucleases, the modified phosphorothioate AO (S-AO) is the most widely used and effective oligonucleotide. However, the end-capped phosphorothioate AOs (ECS-AOs) are increasingly used due to possible toxic and non-specific effects of the S-AO. Other parameters affecting the activity of a GPCR-targeting AO are the length (mostly an 18-, 20- or 21-mer) and the GC-content (mostly varying from 30 to 80%). Interestingly, one-third of the AOs successfully targeting GPCRs possess a GC/AT ratio of 61-70%. AO-induced reductions in GPCR expression levels and function range typically from 21 to 40% and 41 to 50%, respectively. In contrast to many antisense reviews, we therefore conclude that the functional activity of a GPCR after AO treatment correlates mostly with the density of the target receptors (maximum factor 2). However, AOs are no simple tools for experimental use in vivo. Despite successful results in GPCR research, no general guidelines exist for designing a GPCR-targeting AO or, in general, for setting up a GPCR antisense experiment. It seems that the correct choice of a GPCR targeting AO can only be ascertained empirically. This disadvantage of antisense approaches results mostly from incomplete knowledge about the internalisation and mechanism of action of AOs. Together with non-specific effects of AOs and the difficulties of assessing target specificity, this makes the use of AOs a complex approach from which conclusions must be drawn with caution. Further antisense research has to be carried out to ensure the adequate use of AOs for studying GPCR function and to develop antisense as a valuable therapeutic modality.

Overexpression of kinin B1 receptors induces hypertensive response to des-Arg9-bradykinin and susceptibility to inflammation

We demonstrated that rat kinin B(1) receptors displayed a ligand-independent constitutive activity, assessed through inositol phosphate production in transiently or stably transfected human embryonic kidney 293A cells. Substitution of Ala for Asn(130) in the third transmembrane domain resulted in additional constitutive activation of the B(1) receptor. The constitutively active mutant N130A receptor could be further activated by the B(1) receptor agonist des-Arg(9)-bradykinin. To gain insights into the physiological function of the B(1) receptor, we have generated transgenic mice overexpressing wild-type and constitutively active mutant receptors under the control of human cytomegalovirus immediately early gene enhancer/promoter. The rat B(1) receptor transgene expression was detected in the aorta, brain, heart, lung, liver, kidney, uterus, and prostate of transgenic mice by reverse transcription-polymerase chain reaction/Southern blot analysis. Transgenic mice were fertile and normotensive. Overexpression of B(1) receptors exacerbated paw edema induced by carrageenan and rendered transgenic mice more susceptible to lipopolysaccharide-induced endotoxic shock. Interestingly, the hemodynamic response to kinins was altered in transgenic mice, with des-Arg(9)-bradykinin inducing blood pressure increase when intravenously administered. Our study supports an important role for B(1) receptors in modulating inflammatory responses and for the first time demonstrates that B(1) receptors mediate a hypertensive response to des-Arg(9)-bradykinin.

Effects of dexamethasone and protein kinase C inhibitors on the induction of bradykinin B1 mRNA and the bradykinin B1 receptor-mediated contractile response in isolated rat ileum

We detected the expression of inducible bradykinin (BK) B1 receptor mRNA in the rat ileum by the reverse transcriptase-polymerase chain reaction (RT-PCR) method, when the isolated ileum was suspended for at least 1 hr in an aerated Tyrode's solution at 37 degrees. The induction of this mRNA was both time- and temperature-dependent, and was followed by a contractile response to des-Arg9-BK at around 3 hr of incubation; this response increased in magnitude with time and was maximal at 6 hr. In contrast, the contraction in response to BK and the expression of B2 receptor mRNA were constant throughout this 6-hr incubation period. The contraction due to des-Arg9-BK was selectively suppressed by B1 receptor antagonists, i.e. des-Arg9[Leu8]-BK and des-Arg10-HOE140, but not by the B2 antagonists D-Arg-[Hyp3,Thi5,8,D-Phe7]-BK and HOE140. The inducible des-Arg9-BK contractile response was suppressed by continuous in vitro exposure of the ileum to cycloheximide or actinomycin D, but neither inhibitor affected the contraction induced by BK, suggesting that the B1 receptor could be induced de novo. In vitro and ex vivo treatment of the ileum with dexamethasone suppressed the induction of the contractile response to des-Arg9-BK, but had no significant effect on the expression of B1 receptor mRNA. Some protein kinase C inhibitors, i.e. H7 and calphostin C, suppressed the expression of B1 receptor mRNA and diminished the contractile response to des-Arg9-BK. These results suggest that the de novo synthesis of the B1 receptor in the ileum preparation can be up-regulated at the transcriptional level (a process in which a specific isoform of protein kinase C may be involved). Additionally, these data suggest that the contractile response to des-Arg9-BK involves a process sensitive to some post-transcriptional action of dexamethasone.

Kinin B1 and B2 receptor mRNA expression in the hypothalamus of spontaneously hypertensive rats

The central hypertensive effects induced by bradykinin are known to be mediated via B2 receptors, which are present constitutively in the brain. B, receptors are rapidly upregulated during inflammation, hyperalgesia, and experimental diabetes. The hypothalamus plays an important role in the regulation of cardiovascular homeostasis, and all components of kallikrein-kinin system have been identified in this area. Therefore, we analyzed the mRNA expression of B1 and B2 receptors in the hypothalamus of spontaneously hypertensive rats (SHR) by RT-PCR. Male SHR were studied at three different ages corresponding to the three phases in the development of hypertension: (i) 3-4 (prehypertensive), (ii) 7-8 (onset of hypertension), and (iii) 12-13 weeks (established hypertension) after birth, and compared with age-matched Wistar-Kyoto (WKY) rats. At all ages tested, B2 receptor mRNA levels in the hypothalamus of SHR were higher than age-matched WKY rats (p < 0.001). However, the B1 receptor mRNA levels were higher at the established phase of hypertension only. We conclude that B1 and B2 receptor mRNA are differentially expressed in the hypothalamus of SHR and may play different roles in the pathogenesis of hypertension: upregulation of B2 receptor mRNA from early age may participate in the pathogenesis of hypertension, whereas an upregulation of B1 receptor mRNA in the established phase of hypertension may reflect an epiphenomenon in essential hypertension.

Pharmacologic and autoradiographic evidence for an up-regulation of kinin B(2) receptors in the spinal cord of spontaneously hypertensive rats

1. The effects of intrathecally (i.t.) injected kinin B(1) and B(2) receptor agonists and antagonists were measured on mean arterial pressure (MAP) and heart rate (HR) of conscious unrestrained spontaneously hypertensive rats (SHR of 16 weeks old) and age-matched normotensive Wistar Kyoto (WKY). Quantitative in vitro autoradiographic studies were also performed on the thoracic spinal cord of both strains with specific radioligands for B(2) receptors, [(125)I]-HPP-Hoe 140, and B(1) receptors, [(125)I]-HPP-[des-Arg(10)]-Hoe140. 2. Bradykinin (BK) (0.81 - 810 pmol) increased MAP dose-dependently with increases or decreases of HR. The pressor response to BK was significantly greater in SHR. The cardiovascular response to 8.1 pmol BK was reversibly blocked by 81 pmol Hoe 140 (B(2) antagonist) but not by 81 - 810 pmol [des-Arg(10)]-Hoe 140 (B(1) antagonist) in both strains. 3. The B(1) receptor agonist, des-Arg(9)-BK (8100 pmol) produced either no effects or increased MAP with variable effects on HR. These responses were similar in both strains and were reversibly blocked by 81 pmol Hoe 140. Inhibition with 8100 pmol [des-Arg(10)]-Hoe 140 was not specific to B(1) agonist-mediated responses. 4. [(125)I]-HPP-Hoe 140 specific binding sites were predominantly located to superficial laminae of the dorsal horn and were significantly higher in SHR. Low levels of [(125)I]-HPP-[des-Arg(10)]-HOE 140 specific binding sites were found in all laminae of both strains. 5. It is concluded that the hypersensitivity of the cardiovascular response to BK is due to an increased number of B(2) receptors in the spinal cord of SHR and that B(1) receptors are unlikely involved in spinal cardiovascular regulation in SHR.

Vasoactive potential of the b(1) bradykinin receptor in normotension and hypertension

The B(1) type receptor of bradykinin (Bk B(1)R) is believed to be physiologically inert but highly inducible by inflammatory mediators and tissue damage. To explore the potential participation of the Bk B(1)R in blood pressure (BP) regulation, we studied mice with deleted Bk B(2)R gene with induced experimental hypertension, either salt-dependent (subtotal nephrectomy with 0.5% NaCl as drinking water) or renin/angiotensin-dependent (renovascular 2-kidney-1-clip). Compared with the wild-type controls, the B(2)R gene knockout mice had a higher baseline BP (109.7+/-1.1 versus 101.1+/-1.3 mm Hg, P:=0.002), developed salt-induced hypertension faster (in 19.3+/-2.3 versus 27.7+/-2.4 days, P:=0.024), and had a more severe end point BP (148+/-3.7 versus 133+/-3.1 mm Hg, P:<0.05). On the contrary, renovascular hypertension developed to the same extent (149.7+/-4.3 versus 148+/-3.6 mm Hg) and in the same time frame (14+/-2.2 versus 14+/-2.1 days). A bolus infusion of a selective B(1)R antagonist at baseline produced a significant hypertensive response (by 11.4+/-2 mm Hg) in the knockout mice only. Injection of graded doses of a selective B(1)R agonist produced a dose-dependent hypotensive response in the knockout mice only. Assessment of tissue expression of B(1)R and B(2)R genes by reverse transcription-polymerase chain reaction techniques revealed significantly higher B(1)R mRNA levels in the B(2)R knockout mice at all times (normotensive baseline and hypertensive end points). At the hypertensive end points, there was always an increase in B(1)R gene expression over the baseline values. This increase was significant in cardiac and renal tissues in all hypertensive wild-type mice but only in the clipped kidney of the renovascular knockout mice. The B(2)R gene expression in the wild-type mice remained unaffected by experimental manipulations. These results confirm the known vasodilatory and natriuretic function of the Bk B(2)R; they also indicate that in its absence, the B(1)R can become upregulated and assume some of the hemodynamic properties of the B(2)R. Furthermore, they indicate that experimental manipulations to produce hypertension also induce upregulation of the B(1)R, but not the B(2)R, in cardiac and renal tissues.

Endotoxin sensitization to kinin B(1) receptor agonist in a non-human primate model: haemodynamic and pro-inflammatory effects

1. Although endotoxaemia induces kinin B(1) receptors in several animal models, this condition is not documented in primates. This study examined the up-regulation of haemodynamic and pro-inflammatory responses to the B(1) agonist des-Arg(10)-kallidin (dKD) in a non-human primate model. 2. Green monkeys (Cercopithecus aethiops St Kitts) received lipopolysaccharide (LPS; 90 microg kg(-1)) or saline intravenously. After 4 h, anaesthetized monkeys were cannulated via the carotid artery to monitor blood pressure changes following intra-arterial injections of dKD or the B(2) agonist bradykinin (BK). Oedema induced by subcutaneous kinin administration was evaluated as the increase in ventral skin folds in anaesthetized monkeys injected with captopril at 4 h to 56 days post-LPS. 3. LPS increased rectal temperature but did not affect blood pressure after 4 h. dKD reduced blood pressure (E(max): 27+/-4 mmHg; EC(50): 130 pmol kg(-1)) and increased heart rate (E(max): 33 b.p.m.) only after LPS. In contrast, the dose-dependent fall in blood pressure with BK was comparable in all groups. The selective B(1) antagonist [Leu(9)]dKD (75 ng kg(-1) min(-1), intravenously) abolished responses to dKD but not BK. 4. dKD injection induced oedema dose-dependently (2.4+/-0.1 mm at 150 nmol) only following LPS (at 4 h to 12 days but not 56 days). In contrast, BK-induced oedema was present and stable in all monkeys. Co-administration of [Leu(9)]dKD (150 nmol) significantly reduced oedema induced by dKD (50 nmol). 5. These results suggest LPS up-regulation of B(1) receptor effects in green monkeys. This non-human primate model may be suitable for testing new, selective B(1) antagonists with therapeutic potential as anti-inflammatory agents.

Participation of kinins in the captopril-induced inhibition of intimal hyperplasia caused by interruption of carotid blood flow in the mouse

1. In the rat balloon injury model, angiotensin-converting enzyme (ACE) inhibitors prevent vascular remodelling by inhibiting angiotensin II generation and kinin breakdown. We investigated if ACE inhibition also prevents the structural vascular responses to disruption of carotid artery blood flow and if kinin potentiation plays a role in such a protection. 2. Morphometric analysis of the structural alterations caused by ligation of the left carotid artery was performed 14 days after surgery in J129Sv wild-type mice (B(2)(+/+)) drinking normal tap water or water containing captopril (120 mg kg(-1) per day). In addition, the effect of captopril on vascular remodelling was tested in B(2)(+/+) given the bradykinin (BK) B(1) receptor antagonist des-Arg(9)-[Leu(8)]-BK (DALBK, 50 nmol kg(-1) per day, intraperitoneally) or the BK B(2) receptor antagonist D-Arg, [Hyp(3),Thi(5)D-Tic(7),Oic(8)]-BK (icatibant, 1 micromol kg(-1) per day, intraperitoneally), and in B(2) receptor gene knockout mice (B(2)(-/-)). 3. Interruption of blood flow resulted in carotid artery intimal hyperplasia and media thickening in untreated B(2)(+/+), these responses being partially suppressed by captopril. The inhibition of intimal thickening exerted by captopril was reduced in B(2)(+/+) given DALBK or icatibant (P<0.05 for both comparisons) as well as in B(2)(-/-) (P<0.05). Neither antagonism of kinin receptors nor disruption of the B(2) receptor gene altered the suppressive effect of captopril on media thickening. The protection of vascular wall structure was independent of the reduction in blood pressure by captopril. 4. These results demonstrate that kinins participate in the inhibitory effect of captopril on intimal hyperplasia via B(1) and B(2) receptor signalling. Our findings may have important implications in treating vascular remodelling evoked by altered shear stress conditions.