Central bradykininergic system in normotensive and hypertensive rats

Microglia-Mediated Neuroinflammation: A Potential Target for the Treatment of Cardiovascular Diseases

Microglia are tissue-resident macrophages of the central nervous system (CNS). In the CNS, microglia play an important role in the monitoring and intervention of synaptic and neuron-level activities. Interventions targeting microglia have been shown to improve the prognosis of various neurological diseases. Recently, studies have observed the activation of microglia in different cardiovascular diseases. In addition, different approaches that regulate the activity of microglia have been shown to modulate the incidence and progression of cardiovascular diseases. The change in autonomic nervous system activity after neuroinflammation may be a potential intermediate link between microglia and cardiovascular diseases. Here, in this review, we will discuss recent updates on the regulatory role of microglia in hypertension, myocardial infarction and ischemia/reperfusion injury. We propose that microglia serve as neuroimmune modulators and potential targets for cardiovascular diseases.

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.

Kinin-mediated inflammation in neurodegenerative disorders

The mediatory role of kinins in both acute and chronic inflammation within nervous tissues has been widely described. Bradykinin, the major representative of these bioactive peptides, is one of a few mediators of inflammation that directly stimulates afferent nerves due to the broad expression of specific kinin receptors in cell types in these tissues. Moreover, kinins may be delivered to a site of injury not only after their production at the endothelium surface but also following their local production through the enzymatic degradation of kininogens at the surface of nerve cells. A strong correlation between inflammatory processes and neurodegeneration has been established. The activation of nerve cells, particularly microglia, in response to injury, trauma or infection initiates a number of reactions in the neuronal neighborhood that can lead to cell death after the prolonged action of inflammatory substances. In recent years, there has been a growing interest in the effects of kinins on neuronal destruction. In these studies, the overexpression of proteins involved in kinin generation or of kinin receptors has been observed in several neurologic disorders including neurodegenerative diseases such Alzheimer's disease and multiple sclerosis as well as disorders associated with a deficiency in cell communication such as epilepsy. This review is focused on recent findings that provide reliable evidence of the mediatory role of kinins in the inflammatory responses associated with different neurological disorders. A deeper understanding of the role of kinins in neurodegenerative diseases is likely to promote the future development of new therapeutic strategies for the control of these disorders. An example of this could be the prospective use of kinin receptor antagonists.

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.

Role of limbic peptidergic circuits in regulation of arterial pressure, relevant to development of essential hypertension

It is generally accepted that the essential hypertension (EH) is caused by interactions among congenital gene, multiple pathogenetic pressor factors, and disorder of physiologic depressor factors. The central nervous system may play a key role in the development of EH. The underlying mechanisms, however, are not well understood. Studies show that peptidergic transmitters in the limbic forebrain are involved in long-term regulation of arterial pressure and in the pathogenesis of EH. In the limbic forebrain there are peptidergic pressor and depressor circuits. The former includes corticotropin releasing factor-, substance P-, and angiotensin II-circuits; and the latter includes beta-endorphin- and atrial natriuretic peptide-circuits. These circuits extensively interconnect and interact with each other. The altered functions of them may be the pathogenesis of EH. In this review, we focus on the roles of limbic peptidergic circuits in regulation of arterial pressure, relevant to the neurogenetic mechanisms in developing EH.

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.

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.

Des-Arg9-bradykinin increases intracellular Ca2+ in bronchoalveolar eosinophils from ovalbumin-sensitized and -challenged mice

The effects of the selective bradykinin B1 receptor agonist, des-Arg9-bradykinin and the bradykinin B2 receptor agonist, bradykinin were studied on the intracellular free Ca2+ concentration ([Ca2+]i) in murine bronchoalveolar lavage cells from control and ovalbumin-sensitized mice using fura-2 microfluorimetry. The bronchoalveolar lavage cells of control mice, which were predominantly alveolar macrophages, showed an increase in [Ca2+]i in response to bradykinin (1 microM) but not to des-Arg9-bradykinin (1 microM), indicating the presence of functional bradykinin B2 receptors and the absence of B1 receptors. Such elevation in [Ca2+]i induced by bradykinin was totally inhibited by the selective bradykinin B2 receptor antagonist, D-Arg0-Hyp3-Thi5-D-Tic7-Oic8-bradykinin (HOE-140; 10 microM). In contrast, bronchoalveolar lavage cells from ovalbumin-sensitized and -challenged mice significantly responded to both bradykinin and des-Arg9-bradykinin, indicating the presence of both functional bradykinin B1 and B2 receptors. Eosinophils exhibited higher response to des-Arg9-bradykinin (1 microM; 485% increase in [Ca2+]i) compared to bradykinin (1 microM; 163% increase in [Ca2+]i). This des-Arg9-bradykinin-induced [Ca2+]i increase was markedly inhibited by the selective bradykinin B1 receptor antagonist, Ac-Lys-[D-betaNal7, Ile8]des-Arg9-bradykinin (R-715; 10 microM). Des-Arg9-bradykinin neither modified the basal [Ca2+]i in lymphocytes nor in mononuclear cells from ovalbumin-sensitized and challenged mice, while bradykinin produced a [Ca2+]i increase in both cell types. Our results further support the implication of the inducible bradykinin B1 receptors in airway inflammatory response in ovalbumin-sensitized and challenged mice.

Lipopolysaccharide injection into the cerebral ventricle evokes kininogen induction in the rat brain

Kinins, such as bradykinin and Lys-bradykinin, are important mediators in peripheral inflammation. Although the existence of the components necessary for generating kinins has been demonstrated in the brain, a functional role of the kinin-generating system in cerebral inflammation remains to be defined. The aim of the present study was to elucidate whether inflammatory stimuli alter the mRNA levels of components for the kallikrein-kinin system, including kallikreins, kininogens and bradykinin type 2 (B(2)-) receptor in rat brain using the reverse transcription polymerase chain reaction. The intracerebroventricular (i.c.v.) injection of lipopolysaccharide (LPS; 0.25 microg/animal) resulted in the elevation of T-kininogen and high-molecular-weight (H-) kininogen mRNAs in various brain regions within 24 h, prominently in the choroid plexus. The appearance of immunoreactive T-kininogen was demonstrated in the epithelium of the choroid plexus, but not in the matrix and vessels, after i.c.v. injection of LPS. The mRNA levels of kallikreins, such as tissue kallikrein, T-kininogenase and plasma kallikrein, and B(2)-receptor did not change in any brain region following i.c.v. injection of LPS. The levels of cyclooxygenase-2 mRNA in the choroid plexus were increased within 2 h after i.c.v. injection of LPS, and pretreatment with indomethacin (3 microg/animal, i.c.v.) abolished the LPS-induced elevation of T- and H-kininogen mRNAs in the choroid plexus. The i.c.v. injection of prostaglandin E(2) (100 ng/animal) also caused increases in the mRNA levels of T- and H-kininogens in various brain regions, including the choroid plexus. These results suggest that LPS stimulates the induction of kininogens in the brain, especially the choroid plexus, by stimulating the production of arachidonic metabolites such as prostaglandin E(2).

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.

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.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

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.

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

1. We evaluated if the brain bradykinin (BK) B1 receptor is involved in the regulation of blood pressure (BP) in conscious rats. 2. Basal mean BP and HR were 115 +/- 2 and 165 +/- 3 mmHg and 345 +/- 10 and 410 +/- 14 beats min in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR), respectively. Intracerebroventricular (i.c.v.) injection of 1 nmol B1 receptor agonist Lys-desArg9-BK significantly increased the BP of WKY and SHR by 7+/-1 and 19+/-2 mmHg, respectively. One nmol Sar[D-Phe8]-desArg9-BK, a kininase-resistant B1 agonist, increased the BP of WKY and SHR by 19+/-2 and 17+/-2 mmHg, respectively and reduced HR in both strains. 3. I.c.v. injection of 0.01 nmol B1 antagonists, LysLeu8-desArg9-BK or AcLys[D-betaNal7,Ile8]-desArg9-BK (R715), significantly decreased mean BP in SHR (by 9+/-2 mmHg the former and 14+/-3 mmHg the latter compound), but not in WKY. In SHR, the BP response to R715 was associated to tachycardia. 4. I.c.v. Captopril, a kininase inhibitor, increased the BP of SHR, this response being partially prevented by i.c.v. R715 and reversed into a vasodepressor effect by R715 in combination with the B2 antagonist Icatibant. 5. I.c.v. antisense oligodeoxynucleotides (ODNs) targeted to the B1 receptor mRNA decreased BP in SHR, but not in WKY. HR was not altered in either strain. Distribution of fluorescein-conjugated ODNs was detected in brain areas surrounding cerebral ventricles. 6. Our results indicate that the brain B1 receptor participates in the regulation of BP. Activation of the B1 receptor by kinin metabolites could participate in the pathogenesis of hypertension in SHR.

Pathophysiology of the kallikrein-kinin system in mammalian nervous tissue

The nervous system and peripheral tissues in mammals contain a large number of biologically active peptides and proteases that function as neurotransmitters or neuromodulators in the nervous system, as hormones or cellular mediators in peripheral tissue, and play a role in human neurological diseases. The existence and possible functional relevance of bradykinin and kallidin (the peptides), kallikreins (the proteolytic enzymes), and kininases (the peptidases) in neurophysiology and neuropathological states are discussed in this review. Tissue kallikrein, the major cellular kinin-generating enzyme, has been localised in various areas of the mammalian brain. Functionally, it may assist also in the normal turnover of brain proteins and the processing of peptide-hormones, neurotransmitters, and some of the nerve growth factors that are essential for normal neuronal function and synaptic transmission. A specific class of kininases, peptidases responsible for the rapid degradation of kinins, is considered to be identical to enkephalinase A. Additionally, kinins are known to mediate inflammation, a cardinal feature of which is pain, and the clearest evidence for a primary neuronal role exists so far in the activation by kinins of peripherally located nociceptive receptors on C-fibre terminals that transmit and modulate pain perception. Kinins are also important in vascular homeostasis, the release of excitatory amino acid neurotransmitters, and the modulation of cerebral cellular immunity. The two kinin receptors, B2 and B1, that modulate the cellular actions of kinins have been demonstrated in animal neural tissue, neural cells in culture, and various areas of the human brain. Their localisation in glial tissue and neural centres, important in the regulation of cardiovascular homeostasis and nociception, suggests that the kinin system may play a functional role in the nervous system.

Structure-activity studies of B1 receptor-related peptides. Antagonists

We tested several peptides related to des-Arg9-bradykinin as stimulants or inhibitors of B1 (rabbit aorta, human umbilical vein) and B2 (rabbit jugular vein, guinea pig ileum, human umbilical vein) receptors. We also incubated the compounds with purified angiotensin-converting enzyme from rabbit lung to test their resistance to degradation. We evaluated apparent affinities (in terms of the affinity constant pA2) of compounds and their potential residual agonistic activities (alpha E). Bradykinin and des-Arg9-bradykinin were used as agonists for the B2 and B1 receptors, respectively. Degradation of peptides by the angiotensin-converting enzyme was prevented in the presence of a D-residue in position 7 of des-Arg9-bradykinin. Replacement of Pro7 with D-Tic combined with Leu, Ile, Ala, or D-Tic in position 8 led to weak B1 receptor antagonists, some of which had strong residual agonistic activities on the B2 receptor preparations. The use of D-beta Nal in position 7, combined with Ile in position 8 and AcLys at the N-terminal (eg, AcLys[D-beta Nal7, Ile8]des-Arg9-bradykinin) gave the most active B1 receptor antagonist (pA2 of 8.5 on rabbit aorta and human umbilical vein), which is also partially resistant to enzymatic degradation. Extension of the N-terminal end by Sar-Tyr-epsilon Ahx (used for labeling purposes) and even cold-labeling of Tyr with iodine were compatible with high, selective, and specific antagonism of the B1 receptors. We compared some compounds with some already known B1 receptor antagonists to underline the novelty of new peptidic compounds.

Enhanced tumor uptake of carboplatin and survival in glioma-bearing rats by intracarotid infusion of bradykinin analog, RMP-7

OBJECTIVE

Intracarotid infusion of the bradykinin analog, RMP-7, can increase permeability in brain tumor capillaries. This study sought to determine the following: 1) the unidirectional transport, Ki, of radiolabeled [14C]carboplatin into brain tumors with either intravenous or intracarotid RMP-7 infusions; 2) the duration and extent of increased permeability in tumor capillaries during continuous RMP-7 infusions; and 3) the effect on survival of carboplatin combined with RMP-7 treatment in rats with gliomas.

METHODS

Wistar rats with RG2 gliomas were used, and a unidirectional transfer constant, Ki, was determined using quantitative autoradiography. In the survival study, the rats were treated with intra-arterial carboplatin and RMP-7 at Days 5 and 7 after tumor implantation.

RESULTS

Intracarotid infusion of RMP-7 for 15 minutes increased the transport of [14C]carboplatin to tumors by 2.7-fold, as compared with saline infusion alone (P < 0.001). The transports of [14C]dextran and [14C]carboplatin into tumors were significantly higher with 15 minutes of intracarotid infusion of RMP-7 (0.1 microgram/kg/min), compared to those with 10-, 30-, or 60-minute infusions (P < 0.01). Rats treated at Days 5 and 7 after tumor implantation with carboplatin alone (10 mg/kg) exhibited a modest increase in survival at 31 days (37%, compared to < 10% of controls), while those given the combination of carboplatin with RMP-7 exhibited a significantly higher survival rate (74%).

CONCLUSION

Intracarotid infusion of RMP-7 can selectively increase transport of carboplatin into brain tumors and results in higher survival in rats with gliomas. These findings support the use of intracarotid infusion of RMP-7 to enhance the delivery of carboplatin to patients with malignant brain tumors.

Hypertensive effect of tissue kallikrein in rostral ventrolateral medulla is mediated by brain kinins

Microinjections of kallikrein, 0.5-2.0 units, in the rostral ventrolateral medulla (RVLM) of brain increased arterial pressure in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). This effect was significantly greater in SHR. The kinin B2 receptor antagonist icatibant (Hoe 140) blocked the hypertensive responses to kallikrein in both groups and caused greater hypotension and bradycardia in SHR. These results suggest that local kinins in the RVLM act to alter cardiovascular function and may be involved in the maintenance of blood pressure in the SHR.

Pharmacological blood-brain barrier modification for selective drug delivery

Vasoactive agents have been identified through studies of peritumoral edema and effects on systemic capillaries. Abnormal blood-brain barrier or blood-tumor barrier can develop transient increases in permeability with the intraarterial delivery of vasoactive agents. Normal blood-brain barrier resists the effects of these compounds because of a biochemical barrier that may inactivate or become inert to vasoactive agents. Vasoactive compounds, including leukotrienes, bradykinin, and histamine appear to selectively increase permeability in abnormal brain capillaries. Intracarotid infusion of leukotrienes, bradykinin, and other vasoactive agents can increase drug delivery to diseased tissue.

Kinin B1 receptors: a review

The kinin B1 receptor has been initially defined as the one mediating the contractile effect of bradykinin (BK)-related peptides in the isolated rabbit aorta. The B1 receptor is selectively sensitive to kinin metabolites without the C-terminal arginine residue, e.g. des-Arg9-BK and Lys-des-Arg9-BK; it is apparently rapidly up-regulated in immunopathology under the influence of cytokines and is further regulated by growth factors. Progress in the understanding of this pharmacologic entity is reviewed, including the development of B1 receptor agonists and antagonists, binding assays, physiopathological applications and the recent cloning and sequencing of the receptor cDNA.

Brain kallikrein-kinin system abnormalities in spontaneously hypertensive rats

The objective of the present study was to determine whether the brain kallikrein-kinin system differs between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) and if so, whether any detected differences occur before the development of hypertension in SHR. We measured cerebrospinal fluid levels of various components of the system in adult and young prehypertensive SHR and WKY. Cerebrospinal fluid kinin concentration and appearance rate were higher in SHR. Cerebrospinal fluid active kallikrein level and kininogenase activity were also higher in adult SHR. In addition, cerebrospinal fluid kinin concentration and appearance rate were higher in prehypertensive, 5- to 6-week-old SHR compared with age-matched WKY. However, no differences in cerebrospinal fluid kallikrein or kininogenase activity were observed between the two strains of young rats. Cerebrospinal fluid kinin concentration was higher in young versus adult rats of the same strain. In WKY, cerebrospinal fluid kallikrein also decreased with age although cerebrospinal fluid kallikrein concentration did not decrease in young and adult SHR. Together, these data suggest that there is a hyperactive kallikrein-kinin system in the brain of SHR that may contribute to the hypertensive state in this animal model.

Kinins and kinin receptors in the nervous system

Kinins, including bradykinin and kallidin, are peptides that are produced and act at the site of tissue injury or inflammation. They induce a variety of effects via the activation of specific B1 or B2 receptors that are coupled to a number of biochemical transduction mechanisms. In the periphery the actions of kinins include vasodilatation, increased vascular permeability and the stimulation of immune cells and peptide-containing sensory neurones to induce pain and a number of neuropeptide-induced reflexes. Mechanisms for kinin synthesis are also present in the CNS where kinins are likely to initiate a similar cascade of events, including an increase in blood flow and plasma leakage. Kinins are potent stimulators of neural and neuroglial tissues to induce the synthesis and release of other pro-inflammatory mediators such as prostanoids and cytotoxins (cytokines, free radicals, nitric oxide). These events lead to neural tissue damage as well as long lasting disturbances in blood-brain barrier function. Animal models for CNS trauma and ischaemia show that increases in kinin activity can be reversed either by kinin receptor antagonists or by the inhibition of kinin production. A number of other central actions have been attributed to kinins including an effect on pain signalling, both within the brain (which may be related to vascular headache) and within the spinal dorsal horn where primary afferent nociceptors can be stimulated. Kinins also appear to play a role in cardiovascular regulation especially during chronic spontaneous hypertension. Presently, however, direct evidence is lacking for the release of kinins in pathophysiological conditions of the CNS and it is not known whether spinal or central neurones, other than afferent nerve terminals, are sensitive to kinins. A more detailed examination of the effects of kinins and their central pharmacology is necessary. It is also important to determine whether the inhibition of kinin activity will alleviate CNS inflammation and whether kinin receptor antagonists are useful in pathological conditions of the CNS.

Intracarotid infusion of RMP-7, a bradykinin analog: a method for selective drug delivery to brain tumors

The bradykinin analog, RMP-7, was investigated for its ability to selectively increase uptake of molecular tracers in RG2 glial tumors. When infused in low doses (0.1 microgram/kg/min) through the intracarotid artery ipsilateral to RG2 gliomas in rats, RMP-7 significantly increased the permeability of tumor capillaries to methotrexate and to four other tracers of varying molecular weights, compared to intracarotid infusion of vehicle alone. Tracers used to examine permeability included radiolabeled alpha-aminoisobutyric acid (M(r) 103 D), sucrose (M(r) 342 D), methotrexate (M(r) 454.5 D), inulin (M(r) 5000 D), and dextran (M(r) 70,000 D). Permeability was expressed as the unidirectional transfer constant, Ki (microliters/gm/min). The permeability (Ki) of tumors in the RMP-7 group compared to the vehicle control group was as follows: alpha-aminoisobutyric acid, 35.3 +/- 9.11 versus 12.7 +/- 4.56 (p < 0.001); sucrose, 16.5 +/- 3.83 versus 9.28 +/- 3.12 (p < 0.05); methotrexate, 26.3 +/- 10.3 versus 8.98 +/- 6.78 (p < 0.005); inulin, 13.5 +/- 3.23 versus 6.55 +/- 4.32 (p < 0.005); dextran, 15.2 +/- 3.42 versus 1.47 +/- 1.24 (p < 0.001). The permeability of RG2 gliomas to high-molecular-weight dextran (70,000 D) was 10.3-fold higher in the RMP-7 group than in the vehicle control group. Intracarotid infusion of RMP-7 did not significantly increase the blood volume in tumor or brain tissue. The permeability of normal brain capillaries was unaffected by intracarotid infusion of 0.1 microgram/kg/min RMP-7 relative to that achieved in tumor. These data support the idea that intracarotid infusion of RMP-7 will be a useful technique for selective delivery of antitumor compounds to brain tumors.

Intracarotid infusion of bradykinin selectively increases blood-tumor permeability in 9L and C6 brain tumors

This study investigated the effects of bradykinin on blood-tumor barrier (BTB) permeability in transplanted 9L gliosarcomas (9L) and C6 gliomas (C6) in rats. Permeability, expressed as the unidirectional transfer constant, Ki (microliter/g/min), was measured by quantitative autoradiography. Tracers used to examined permeability included radiolabeled alpha-aminoisobutyric acid ([14C]AIB), sucrose ([14C]sucrose) and dextran ([14C]dextran). Intracarotid infusion of bradykinin (10 mg/kg/min) significantly increased the BTB permeability in both 9L and C6 tumors to [14C]AIB and [14C]sucrose, but did not increase permeability to [14C]dextran. Blood-brain barrier (BBB) permeability in normal (non-tumor) brain was not significantly increased to any of the tracers by intracarotid bradykinin infusion. Ki values for [14C]AIB, [14C]sucrose and [14C]dextran of 9L tumors in the bradykinin group versus control group were 41.6 +/- 12.6 vs. 24.8 +/- 6.30 (P < 0.02), 17.5 +/- 9.34 vs. 9.05 +/- 4.36 (P < 0.05), and 3.90 +/- 2.59 vs. 2.42 +/- 1.76, respectively (mean +/- S.D.). Ki values to [14C]AIB, [14C]sucrose and [14C]dextran of C6 tumors in the bradykinin group versus control group were 41.4 +/- 19.0 vs. 19.5 +/- 11.4 (P < 0.01), 18.0 +/- 8.88 vs. 7.06 +/- 3.05 (P < 0.01), and 4.07 +/- 1.45 vs. 2.27 +/- 1.26, respectively (mean +/- S.D.). Intracarotid infusion of bradykinin did not significantly increase the blood volume in tumor or brain tissue despite its known vasodilative effect. Intracarotid infusion of bradykinin may be a useful technique for selective delivery of compounds to brain tumors.

Bradykinin selectively opens blood-tumor barrier in experimental brain tumors

Bradykinin, infused in low doses (10 micrograms/kg/min) through the carotid artery ipsilateral to RG2 glioma in rats, significantly increased the permeability in tumor capillaries to six different tracers of varying molecular weights compared with intracarotid infusion of saline alone. Permeability in normal brain capillaries was not significantly increased by intracarotid bradykinin infusion. Tracers used to examined permeability included radiolabeled alpha-aminoisobutyric acid (AIB; MW 103), sucrose (MW 342.3), inulin (MW 5000), and dextran (MW 70,000), horseradish peroxidase (HRP) and Evans blue (EB). Permeability was expressed as the unidirectional transfer constant K(i) (microliter/g/min). The permeabilities (K(i)) of tumors in the bradykinin group versus the control saline group for AIB, sucrose, inulin, and dextran were 25.91 +/- 6.78 vs. 13.95 +/- 4.29 (p < 0.01), 17.90 +/- 2.65 vs. 10.75 +/- 4.55 (p < 0.01), 23.92 +/- 6.99 vs. 6.20 +/- 4.37 (p < 0.01), and 17.84 +/- 1.00 vs. 1.47 +/- 1.24 (p < 0.001), respectively (mean +/- SD). Permeability of RG2 gliomas to high molecular weight dextran (70,000) was 12-fold higher in the bradykinin group than in the saline infusion group. Intracarotid infusion of bradykinin did not significantly increase the blood volume in tumor or brain tissue despite its known vasodilative effect. The permeability of normal brain capillaries was unaffected by intracarotid bradykinin infusion. The increased permeability was reversed 20 min after stopping the intracarotid infusion. Electron microscopic and gross qualitative analysis was performed using HRP and EB. Intracarotid bradykinin infusion increased HRP and EB within tumor tissue but not normal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)