Pharmacology and cardiovascular implications of the kinin-kallikrein system

A Potent Inhibitor of Aminopeptidase P2 Reduces Reperfusion Injury in Models of Myocardial Infarction and Stroke

During a myocardial infarction or ischemic stroke, blood flow to the heart or brain is partially blocked. This results in reduced delivery of oxygen and nutrients and, ultimately, tissue damage. Initial treatment involves removing the clot and restoring blood flow (reperfusion). However, this treatment is not as effective as one would hope because the reperfusion process itself can cause a different type of damage (reperfusion injury) that contributes up to 50% of the total damage. Bradykinin is an autocoid that is released from blood vessel endothelial cells during ischemia and reperfusion and has the potential to prevent reperfusion injury. However, bradykinin is rapidly inactivated by enzymes on endothelial cells, limiting its beneficial effects. One of these enzymes is aminopeptidase P2. We designed a potent and specific inhibitor of aminopeptidase P2 called ST-115, [(S)-2-mercapto-4-methylpentanoyl]-4(S)-fluoro-Pro-Pro-3(R)-beta-Pro. When ST-115 is administered intravenously at the start of reperfusion, it reduces bradykinin degradation. This increases bradykinin's concentration in the capillaries and enhances its protective effects. We tested ST-115 in a mouse model of myocardial infarction and found that the damaged area of the heart was reduced by 58% compared with mice given saline. In a rat model of ischemic stroke, ST-115 reduced functional deficits in a skilled walking test by 60% and reduced brain edema by 51%. It reduced brain infarct size by 48% in a major subset of rats with small strokes. The results indicate that ST-115 can ameliorate reperfusion injury and can ultimately serve as a therapeutic for acute myocardial infarction and ischemic stroke. SIGNIFICANCE STATEMENT: We have shown that our aminopeptidase P2 inhibitor, ST-115, can reduce tissue injury caused by episodes of ischemia followed by reperfusion. It was successful in rodent models of myocardial infarction and stroke. The clinical use would involve the intravenous administration of ST-115 at the induction of reperfusion. In the case of stroke, the successful technique of thrombectomy could be combined with ST-115 administration to simultaneously reduce both ischemic and reperfusion injury.

Cryo-EM structures of human bradykinin receptor-Gq proteins complexes

The type 2 bradykinin receptor (B2R) is a G protein-coupled receptor (GPCR) in the cardiovascular system, and the dysfunction of B2R leads to inflammation, hereditary angioedema, and pain. Bradykinin and kallidin are both endogenous peptide agonists of B2R, acting as vasodilators to protect the cardiovascular system. Here we determine two cryo-electron microscopy (cryo-EM) structures of human B2R-G_q in complex with bradykinin and kallidin at 3.0 Å and 2.9 Å resolution, respectively. The ligand-binding pocket accommodates S-shaped peptides, with aspartic acids and glutamates as an anion trap. The phenylalanines at the tail of the peptides induce significant conformational changes in the toggle switch W283^6.48, the conserved PIF, DRY, and NPxxY motifs, for the B2R activation. This further induces the extensive interactions of the intracellular loops ICL2/3 and helix 8 with G_q proteins. Our structures elucidate the molecular mechanisms for the ligand binding, receptor activation, and G_q proteins coupling of B2R.

Bradykinin-Potentiating Activity of a Gamma-Irradiated Bioactive Fraction Isolated from Scorpion (Leiurus quinquestriatus) Venom in Rats with Doxorubicin-Induced Acute Cardiotoxicity: Favorable Modulation of Oxidative Stress and Inflammatory, Fibrogenic and Apoptotic Pathways

Although doxorubicin (Dox) is a backbone of chemotherapy, the search for an effective and safe therapy to revoke Dox-induced acute cardiotoxicity remains a critical matter in cardiology and oncology. The current study was the first to explore the probable protective effects of native and gamma-irradiated fractions with bradykinin-potentiating activity (BPA) isolated from scorpion (Leiurus quinquestriatus) venom against Dox-induced acute cardiotoxicity in rats. Native or irradiated fractions (1 μg/g) were administered intraperitoneally (i.p.) twice per week for 3 weeks, and Dox (15 mg/kg, i.p.) was administered on day 21 at 1 h after the last native or irradiated fraction treatment. Electrocardiographic (ECG) aberrations were ameliorated in the Dox-treated rats pretreated with the native fraction, and the irradiated fraction provided greater amelioration of ECG changes than that of the native fraction. The group pretreated with native protein with BPA also exhibited significant improvements in the levels of oxidative stress-related, inflammatory, angiogenic, fibrogenic, and apoptotic markers compared with those of the Dox group. Notably, the irradiated fraction restored these biomarkers to their normal levels. Additionally, the irradiated fraction ameliorated Dox-induced histological changes and alleviated the severity of cardiac injury to a greater extent than that of the native fraction. In conclusion, the gamma-irradiated detoxified fraction of scorpion venom elicited a better cardioprotective effect than that of the native fraction against Dox-induced acute cardiotoxicity in rats.

The modular nature of bradykinin-potentiating peptides isolated from snake venoms

Bradykinin-potentiating peptides (BPPs) are molecules discovered by Sergio Ferreira – who found them in the venom of Bothrops jararaca in the 1960s – that literally potentiate the action of bradykinin in vivo by, allegedly, inhibiting the angiotensin-converting enzymes. After administration, the global physiological effect of BPP is the decrease of the blood pressure. Due to this interesting effect, one of these peptides was used by David Cushman and Miguel Ondetti to develop a hypotensive drug, the widely known captopril, vastly employed on hypertension treatment. From that time on, many studies on BPPs have been conducted, basically describing new peptides and assaying their pharmacological effects, mostly in comparison to captopryl. After compiling most of these data, we are proposing that snake BPPs are ‘modular’ peptidic molecules, in which the combination of given amino acid ‘blocks’ results in the different existing peptides (BPPs), commonly found in snake venom. We have observed that there would be mandatory modules (present in all snake BPPs), such as the N-terminal pyroglutamic acid and C-terminal QIPP, and optional modules (amino acid blocks present in some of them), such as AP or WAQ. Scattered between these modules, there might be other amino acids that would ‘complete’ the peptide, without disrupting the signature of the classical BPP. This modular arrangement would represent an important evolutionary advantage in terms of biological diversity that might have its origins either at the genomic or at the post-translational modification levels. Regardless of the modules’ origin, the increase in the diversity of peptides has definitely been essential for snakes’ success on nature.

Metabolites as novel biomarkers for childhood obesity-related traits in Mexican-American children

BACKGROUND/OBJECTIVES

Although newer approaches have identified several metabolites associated with obesity, there is paucity of such information in paediatric populations, especially among Mexican-Americans (MAs) who are at high risk of obesity. Therefore, we performed a global serum metabolite screening in MA children to identify biomarkers of childhood obesity.

METHODS

We selected 15 normal-weight, 13 overweight and 14 obese MA children (6-17 years) and performed global serum metabolite screening using ultra-performance liquid chromatography/quadruple orthogonal acceleration time of flight tandem micro mass spectrometer. Metabolite values were analysed to assess mean differences among groups using one-way analysis of variance, to test for linear trend across groups and to examine Pearson's correlations between them and seven cardiometabolic traits (CMTs): body mass index, waist circumference, systolic blood pressure, diastolic blood pressure, homeostasis model of assessment-insulin resistance, triglycerides and high-density lipoprotein cholesterol.

RESULTS

We identified 14 metabolites exhibiting differences between groups as well as linear trend across groups with nominal statistical significance. After adjustment for multiple testing, mean differences and linear trends across groups remained significant (P < 5.9 × 10(-5) ) for L-thyronine, bradykinin and naringenin. Of the examined metabolite-CMT trait pairs, all metabolites except for 2-methylbutyroylcarnitine were nominally associated with two or more CMTs, some exhibiting significance even after accounting for multiple testing (P < 3.6 × 10(-3) ).

CONCLUSIONS

To our knowledge, this study - albeit pilot in nature - is the first study to identify these metabolites as novel biomarkers of childhood obesity and its correlates. These findings signify the need for future systematic investigations of metabolic pathways underlying childhood obesity.

KLK1 and ZG16B proteins and arginine-proline metabolism identified as novel targets to monitor atherosclerosis, acute coronary syndrome and recovery

We pursued here the identification of specific signatures of proteins and metabolites in urine which respond to atherosclerosis development, acute event and/or recovery. An animal model (rabbit) of atherosclerosis was developed and molecules responding to atherosclerosis silent development were identified. Those molecules were investigated in human urine from patients suffering an acute coronary syndrome (ACS), at onset and discharge. Kallikrein1 (KLK1) and zymogen granule protein16B (ZG16B) proteins, and l-alanine, l-arabitol, scyllo-inositol, 2-hydroxyphenilacetic acid, 3-hydroxybutyric acid and N-acetylneuraminic acid metabolites were found altered in response to atherosclerosis progression and the acute event, composing a molecular panel related to cardiovascular risk. KLK1 and ZG16B together with 3-hydroxybutyric acid, putrescine and 1-methylhydantoin responded at onset but also showed normalized levels at discharge, constituting a molecular panel to monitor recovery. The observed decreased of KLK1 is in alignment with the protective mechanism of the kallikrein-kinin system. The connection between KLK1 and ZG16B shown by pathway analysis explains reduced levels of toll-like receptor 2 described in atherosclerosis. Metabolomic analysis revealed arginine and proline metabolism, glutathione metabolism and degradation of ketone bodies as the three main pathways altered. In conclusion, two novel urinary panels of proteins and metabolites are here for the first time shown related to atherosclerosis, ACS and patient's recovery.

Involvement of bradykinin and prostaglandins in the diuretic effects of Achillea millefolium L. (Asteraceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Achillea millefolium L. (Asteraceae), popularly known as "mil-folhas", is well recognized and widely used in Brazilian folk medicine to treat heart and kidney disorders. Among its popularly described effects are diuretic and hypotensive actions.

AIM OF THE STUDY

The diuretic activity of Achillea millefolium L. extracts and its semi-purified fractions, as well as the mechanisms involved, were evaluated in male Wistar rats.

MATERIAL AND METHODS

An aqueous extract (AEAM, 125-500 mg/kg), hydroethanolic extract (HEAM, 30-300 mg/kg), dichloromethane subfractions (DCM-2, 10 and 30 mg/kg), or hydrochlorothiazide (10mg/kg), were orally administered and the animals were kept in metabolic cages for 8h for urine collection. To evaluate the involvement of bradykinin and prostaglandins in the diuretic action of Achillea millefolium, selected groups of rats received HOE-140 (1.5mg/kg, i.p.) or indomethacin (5mg/kg, p.o.), before treatment with a DCM-2 subfraction (30 mg/kg). The urinary volume, conductivity, pH, density and electrolyte excretion were measured.

RESULTS

Similar to hydrochlorothiazide, both HEAM and DCM-2, but not AEAM, increased urinary volume and the excretion of Na(+) and K(+) when compared with the control group (vehicle). The diuretic effect of DCM-2 was abolished by HOE-140 (a bradykinin B2 receptor antagonist), as well as by indomethacin (a cyclooxygenase inhibitor).

CONCLUSION

The present study reveals that extracts obtained from Achillea millefolium are able to effectively increase diuresis when orally administered in rats. This effect depends on both the activation of bradykinin B2 receptors and the activity of cyclooxygenases.

The kinin-kallikrein system: physiological roles, pathophysiology and its relationship to cancer biomarkers

The kinin-kallikrein system (KKS) is an endogenous multiprotein cascade, the activation of which leads to triggering of the intrinsic coagulation pathway and enzymatic hydrolysis of kininogens with the consequent release of bradykinin-related peptides. This system plays a crucial role in inflammation, vasodilation, smooth muscle contraction, cardioprotection, vascular permeability, blood pressure control, coagulation and pain. In this review, we will outline the physiology and pathophysiology of the KKS and also highlight the association of this system with carcinogenesis and cancer progression.

Effect of Montelukast on bradykinin-induced contraction of isolated tracheal smooth muscle of guinea pig

AIM

To explore the effect of montelukast on bradykinin-induced tracheal smooth muscle contraction of isolated guinea pig trachea.

STUDY DESIGN

To study the effect of bradykinin in the absence and in the presence of montelukast on the isolated tracheal smooth muscle of a guinea pig pretreated with indomethacin (10(-6)M), phentolamine (10(-5)M), and propranalol (10(-6)M), to eliminate the effect of endogenous prostaglandins and catecholamines. The trachealis smooth muscle activity was recorded through the Isometric Force Displacement Transducer on a Four Channel Oscillograph. A cumulative dose-response relationship was demonstrated by adding successive doses of bradykinin on the tracheal strips, starting with 11 μg to 77 μg of 10(-4) concentration. A similar procedure was repeated in the presence of montelukast 0.5 μg/ml, which, was equal to approximate C(max) achieved in vivo with a 10 mg oral dose of montelukast, and in the presence of 1 μg/ml of montelukast.

STATISTICAL ANALYSIS

Data was expressed as mean ± standard error (SEM), and was analyzed using the SPSS version 15. A P value of less than 0.05 was considered significant.

RESULTS

Bradykinin produced a dose-dependent, reversible contraction of isolated tracheal smooth muscle. Montelukast significantly reduced the bradykinin-induced tracheal smooth muscle reactivity and shifted the bradykinin curve to the right and downwards, in the presence of both concentrations of montelukast. The mean magnitude of response achieved with 77 μg of bradykinin in the absence of montelukast was 39 mm ± 6.26, in the presence of 0.5 μg/ml of montelukast it was 24.17 mm ± 4.11, and in the presence of 1 μg/ml of montelukast it was 13 mm ± 2.6.

CONCLUSION

It is concluded that montelukast significantly inhibits, in a dose-dependent manner, the bradykinin-induced contraction of the guinea pig tracheal smooth muscle, and alludes to an interaction between the bradykinin and leukotriene mediators.

A Novel Category of Anti-Hypertensive Drugs for Treating Salt-Sensitive Hypertension on the Basis of a New Development Concept

Terrestrial animals must conserve water and NaCl to survive dry environments. The kidney reabsorbs 95% of the sodium filtered from the glomeruli before sodium reaches the distal connecting tubules. Excess sodium intake requires the renal kallikrein-kinin system for additional excretion. Renal kallikrein is secreted from the distal connecting tubule cells of the kidney, and its substrates, low molecular kininogen, from the principal cells of the cortical collecting ducts (CD). Formed kinins inhibit reabsorption of NaCl through bradykinin (BK)-B₂ receptors, localized along the CD. Degradation pathway of BK by kinin-destroying enzymes in urine differs completely from that in plasma, so that ACE inhibitors are ineffective. Urinary BK is destroyed mainly by a carboxypeptidase-Y-like exopeptidase (CPY) and partly by a neutral endopeptidase (NEP). Inhibitors of CPY and NEP, ebelactone B and poststatin, respectively, were found. Renal kallikrein secretion is accelerated by potassium and ATP-sensitive potassium (KATP) channel blockers, such as PNU-37883A. Ebelactone B prevents DOCA-salt hypertension in rats. Only high salt intake causes hypertension in animals deficient in BK-B2 receptors, tissue kallikrein, or kininogen. Hypertensive patients, and spontaneously hypertensive rats, excrete less kallikrein than normal subjects, irrespective of races, and become salt-sensitive. Ebelactone B, poststatin, and KATP channel blockers could become novel antihypertensive drugs by increase in urinary kinin levels. Roles of kinin in cardiovascular diseases were discussed.

Regulation of the epithelial calcium channel TRPV5 by extracellular factors

PURPOSE OF REVIEW

Recent studies have greatly increased our knowledge concerning the regulation of renal calcium handling. This review focuses on newly identified calciotropic factors present in the pro-urine and the mechanisms by which they control the transient receptor potential channel vanilloid subtype 5 (TRPV5) which forms the gatekeeper of active renal calcium reabsorption.

RECENT FINDINGS

The antiaging hormone klotho regulates TRPV5 activity via a novel mechanism modifying its glycosylation status, thereby entrapping the channel at the cell surface. Functional characterization of tissue kallikrein knockout mice revealed that these animals exhibit a pronounced hypercalciuria, comparable to the calcium leak observed in TRPV5 knockout mice. Recently, it has been demonstrated that tissue kallikrein stimulates active calcium reabsorption via the bradykinin receptor type 2 pathway involving protein kinase C-dependent activation of TRPV5. Finally, the extracellular pH appears to act as a dynamic switch controlling cell surface expression of TRPV5.

SUMMARY

Unraveling the molecular mechanisms of TRPV5 channel regulation by the antiaging hormone klotho, tissue kallikrein and extracellular pH demonstrated the existence of novel regulatory mechanisms of active calcium reabsorption acting from the tubular lumen.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

Modulation of kinin B1 receptor expression by endogenous angiotensin II in hypertensive rats

We investigated the expression and localization of B1 receptor in tissues of rats submitted to a renin-dependent model of hypertension (2K-1C), and analyzed the influence of endogenous Ang II in modulating the in vivo expression of these receptors. B1 mRNA levels in the heart, kidney and thoracic aorta were quantified by real time PCR, B1 receptor protein expression was assessed by immunohistochemistry, plasma Ang II levels were analyzed by radioimmunoassay and the effects of AT1 receptor blockade were determined after losartan treatment. 2K-1C rats presented a marked increase in Ang II levels when compared to sham-operated rats. In parallel, cardiac- (but not renal and aortic) B1 mRNA levels were 15-fold higher in 2K-1C than in sham rats. In 2K-1C, B1 expression was detected in the endothelium of small cardiac arteries and in cardiomyocytes. Losartan completely reverted the increased B1 mRNA levels and significantly decreased the protein expression observed in 2K-1C rats, despite reducing, but not normalizing blood pressure. We conclude that in the 2K-1C rat, induction of cardiac B1 receptor might be tightly linked to AT1 receptor activation. These data suggest the existence of a new site of interaction between kinins and angiotensins, and might provide important contributions for a better understanding of the pathophysiology of hypertension.

Effects of candesartan and enalaprilat on the organ-specific microvascular permeability during haemorrhagic shock in rats

BACKGROUND

To counteract the contribution of angiotensin II to shock-induced ischaemic organ damage pharmacologic blockade of the renin-angiotensin-system (RAS) is currently under investigation. To evaluate potential side-effects of RAS blockade regarding capillary leak, we studied alterations in microvascular permeability in various organs during haemorrhagic shock (HS) in rats pretreated with candesartan (AT(1)-receptor antagonism) or enalaprilat (ACE-inhibition).

METHODS

Thirty-eight instrumented and anaesthetized animals received either candesartan, enalaprilat or placebo. Within each of the three groups 6-7 animals were exposed to HS and 6 animals of each group served as normovolaemic controls. After 30 min of shock, 50 mg kg(-1) Evans blue (EB) was injected i.v. followed by a distribution period of 20 min. Exsanguination was performed with saline, before harvesting organs to quantify albumin-bound EB extravasation.

RESULTS

To reduce cardiac output from 37.5 (1.3) to 20.4 (1.1) ml min(-1) [mean (SEM)] in the shock groups, withdrawal of 4.0 (0.25) ml [mean (SEM)] blood was necessary. Simultaneously mean arterial pressure decreased from 77.5 (3.2) to 36.1 (2) mm Hg. Serum lactate increased significantly from 1.3 (0.1) to 3.5 (0.24) mmol litre(-1). Treatment with candesartan increased EB extravasation in the kidney in normovolaemic controls. Specific AT(1) and ACE-blockade before acute non-resuscitated HS significantly increased EB extravasation in the rat ileum by 53 and 66%, respectively.

CONCLUSION

This observation of increased microvascular albumin extravasation should be borne in mind for any interventional use of candesartan or enalaprilat during circulatory stress.

Captopril effect on prostaglandin E2, thromboxane B2 and proteinuria in lupus nephritis patients

OBJECTIVE

High urinary Prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) levels have been reported in lupus nephritis (LN). Captopril diminishes proteinuria and improves glomerular filtration rate (GFR), and may have effect on immune function. We evaluate captopril effect on urinary PGE2, and TxB2.

METHODS

Eighteen LN patients were randomly assigned to two groups. Group 1 received only prednisone plus cyclophosphamide. Group 2 received also captopril. Serum creatinine, GFR, RPF, urinary proteins, PGE2 and TxB2, were assessed.

RESULTS

There were no differences between the initial and final assessments in Group 1. Group 2 showed a significant decrement in proteinuria (p=0.003) and serum creatinine (p=0.01) at the end of the study. PGE2 decreased significantly when compared with the initial value (p=0.02).

CONCLUSION

Captopril plus usual treatment, improved serum creatinine and decreased proteinuria in parallel with prostaglandin E2 reduction. This effect is not related to changes in GFR or RPF. Captopril may have an immunomodulatory effect on local inflammatory processes in lupus nephritis.

Aprotinin suppresses ACE-inhibitor cough triggered by TAME-esterase

N-alpha-Tosyl l-arginine methyl ester [TAME]-esterase appears to be an important biochemical marker, which displays potent contractile properties on bronchial tissues and aorta in vitro. TAME-esterase induced contractions have been shown to be mediated via a nitric oxide-cyclic GMP pathway. TAME-esterase has also been described to be a possible new cardiovascular risk factor among smokers. TAME-esterase has been reported to be an enzyme, which is involved during the sequence of events leading to the activation of the kinin-kallikrein system. Use of aprotinin (a kallikrein inhibitor) as well as aspirin and indomethacin (prostaglandin inhibitors) have shown that there is an inter-dependent relationship between the kinin-kallikrein system and the cyclo-oxygenase pathway involved during the sequence of reactions leading to TAME-esterase induced contractions. Our findings also lend support to the concept of calcium antagonism whereby verapamil, and nifedipine, mimicked in reversible fashion the effects of Ca2+ withdrawal on muscle excitability during TAME-esterase induced contractions on rat aorta in vitro. We concluded that the effects of captopril, an ACE inhibitor, on TAME-esterase induced contractions could thus be due to the degradation of bradykinin by the enzyme kininase being blocked. This paper proposes an integrated model of possible biochemical-pharmacological pathways, which involve events leading to TAME-esterase induced contractions. We hypothesize that TAME-esterase induced cough through sensitization of airway sensor nerves in hypertensive patients taking angiotensin-converting enzyme inhibitors can be inhibited by aprotinin.

Modulation of nitric oxide and 6-keto-prostaglandin F(1alpha) production in bovine aortic endothelial cells by conjugated linoleic acid

Conjugated linoleic acid (CLA) refers to a group of polyunsaturated fatty acids that exist as positional (18:2) and stereo (cis/trans) isomers of conjugated dienoic octadecadienoate. Reports consistently indicate that CLA may inhibit both the onset and progression of atherosclerosis, via an as yet unknown mechanism(s). In an effort to identify the putative biochemical effects of CLA on bovine aortic endothelial cells (BAECs), the authors examined both the temporal and dose-dependent effects of a commercial CLA isomeric mixture on the expression and enzymatic function of endothelial nitric oxide synthase (eNOS) and cyclooxygenase-I/II (COX-I/II) in these cells. Initial investigations indicated that CLA mix (0 to 10 microg/mL, 0 to 24 h) failed to regulate either the expression or activity of eNOS in BAECs under basal conditions. Pretreatment of BAECs with CLA mix (10 microg/mL) for either 3 or 24 h, followed by incubation with 5 microM bradykinin (BK) for 3 h, however, increased BK-stimulated nitrite release by 2.4 +/- 0.6- and 3.0 +/- 0.4-fold, respectively, more than control cells (BK-stimulation without CLA pretreatment). Under basal conditions, CLA mix (10 microg/mL, 0 to 24 h) had no significant effect on either COX-I or COX-II expression, genes that could be readily induced in response to hemodynamic stimuli. CLA could, however, significantly attenuate BAEC release of 6-keto-prostaglandin F(1alpha) (6k-PGF(1alpha)), a stable breakdown product of prostaglandin I2 (PGI2) within the cyclooxygenase pathway, in a dose- and time-dependent manner. In conclusion, therefore, the results suggest that CLA may potentiate agonist-stimulated eNOS activation whilst attenuating COX-dependent PGI2 synthesis in BAECs. This ability to increase agonist-stimulated nitric oxide (NO) levels, whilst reducing production of inflammatory mediators within vascular ECs, supports a putative atheroprotective role for CLA and provides an important biochemical insight into its purported ability to modulate endothelium-mediated vascular homeostasis.

Combined blockade of AT1-receptors and ACE synergistically potentiates antihypertensive effects in SHR

OBJECTIVES AND DESIGN

To check whether antihypertensive effects are additive or synergistic upon blockade of both angiotensin (AT1)-receptors and angiotensin-converting enzyme (ACE), spontaneously hypertensive rats (SHR) were treated with candesartan-cilexetil (0.1-30 mg/kg per day), ramipril (0.03-10 mg/kg per day), the calcium-antagonist mibefradil (1-150 mg/kg per day) or combinations thereof. Systolic blood pressure (SBP), left ventricular weight (LVW) and the cardiac activity/mRNA levels of ACE were determined.

RESULTS

SBP was decreased by candesartan-cilexetil [inhibitory concentration (IC50) (mg/kg): 2.47], ramipril (1.97), mibefradil (4.41), candesartan-cilexetil/ramipril (0.68), and candesartan-cilexetil/mibefradil (5.68). Combining candesartan-cilexetil with ramipril increased SBP reduction synergistically rather than additively, since the dose-response curve was shifted 6.6-fold leftwards compared to a hypothetically generated additive curve, calculated by summing up the doses and corresponding effects of the ramipril and candesartan-cilexetil monotreatment regimes. A total threshold dose < 5.14 mg/kg (derived from dose-response curves) was found to exert synergistic effects when candesartan-cilexetil was combined with ramipril. Antihypertensive effects of mibefradil can not be increased when combined with candesartan-cilexetil. When LVW was correlated with SBP reduction, regression lines of candesartan-cilexetil, ramipril and their combination were congruent, while that for mibefradil was significantly flatter and became steeper under candesartan-cilexetil co-administration. Cardiac ACE activity was greatly reduced by ramipril independently of SBP reduction and dosage. With SBP-ineffective doses of ramipril, cardiac ACE mRNA levels were doubled, indicating a positive feedback mechanism. The increase in ACE mRNA was renormalized when SPB-effective ramipril doses were applied, suggesting a blood pressure-dependent regulation of cardiac ACE expression.

CONCLUSIONS

Since synergy was observed only after combining low doses of ramipril and candesartan-cilexetil, prospective clinical trials should be performed on a low-dose combination, revealing the antihypertensive/antiproliferative benefits.

Bradykinin B 1 Receptor Expression Induced by Tissue Damage in the Rat Portal Vein

The bradykinin B1 receptor (B1R) is normally absent under physiological conditions, but is highly inducible during inflammatory conditions or following tissue damage. The present study attempted to determine some of the mechanisms underlying B1R upregulation following tissue injury in rat portal vein. Damage induced by tissue isolation and in vitro incubation caused a significant and time-dependent increase in des-Arg9-bradykinin (des-Arg9-BK) responsiveness that paralleled the B1R mRNA expression, as confirmed by real-time quantitative PCR. In vitro incubation of rat portal vein also induced the activation of some members of the mitogen activated protein kinase (MAPK) family, namely, extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK), and p38 MAPK, an effect accompanied by degradation of the inhibitory protein IkappaBalpha and translocation of nuclear transcription factor-kappaB (NF-kappaB) to the nucleus. The blockade of p38 MAPK, JNK or NF-kappaB, but not ERK pathways with selective inhibitors, resulted in a significant reduction of the upregulated contractile response caused by the selective B1R agonist des-Arg9-BK, and largely prevented the induction of B1R mRNA expression in the rat portal vein. Together, these results demonstrate that in vitro tissue damage induces activation of several intracellular signaling pathways that have a key role in the control of B1R expression. B1R could exert a pivotal role in the development of the cardiovascular response associated with vascular damage.

Evidence for bradykinin as a stimulator of thirst

Angiotensin-converting enzyme inhibition (ACEI) with captopril has been shown to increase water intake and urine output in rats, but the mechanism is unknown. ACEI impairs the conversion of ANG I to ANG II, a dipsogenic hormone, and impairs the degradation of bradykinin. The goal of this study was to examine the role of bradykinin in the polydipsia and polyuria associated with ACEI. Male Sprague-Dawley rats received captopril (CPT; 20 mg.kg(-1).day(-1)) in ground chow for 48 h. Water intake, food intake, and urine output were monitored and compared with control rats (CTL), rats receiving captopril treatment with limited water intake (CPT-LIM), and rats receiving captopril treatment with ad libitum water intake plus 24-h treatment with the bradykinin antagonist B-9430 (CPT-BK1). CPT rats consumed significantly more water and produced more urine vs. CTL. Urine osmolality was significantly decreased in CPT rats vs. CTL. Inner medullary aquaporin-2 (AQP2) protein abundance was also markedly decreased in CPT rats vs. CTL. These findings were reversed in CPT-LIM rats, suggesting captopril-induced primary polydipsia. CPT-BKI rats demonstrated parameters no different from CTL despite ad libitum water intake. Mean arterial pressure and 24-h creatinine clearance did not differ among groups. We conclude that ACEI with captopril induces primary polydipsia despite impaired production of the dipsogen ANG II and that this primary increase in water intake is likely the cause of the decreased protein abundance of inner medullary AQP2. Furthermore, this dipsogenic effect was reversed by antagonism of bradykinin, thus implicating this hormone in thirst regulation in the rat.

Renal kallikrein-kinin system damage and salt sensitivity: insights from experimental models

The importance of tubulointerstitial injury in the pathophysiology of human essential hypertension, and particularly salt sensitivity, is increasingly recognized. Since the renal kallikrein-kinin system (KKS) is located in the tubulointerstitial region of the kidney it is reasonable to expect that injury to this area, whatever the cause, may impair KKS production and compromise its role in blood pressure regulation. In this review we discuss evidence of injury in the renal kallikrein-producing structures in three different experimental models characterized by prominent tubulointerstitial lesions: subtotal nephrectomy; inhibition of nitric oxide synthase; and overload proteinuria. These three experimental models have in common the development of important tubulointerstitial damage and salt-sensitive hypertension expressed after the initial injury has ceased. In these three models, reduced KKS activity may contribute to the establishment of a pathophysiologic state characterized by unopposed hyperactivity of the renin-angiotensin system, resulting in salt retention.

Effects of aspirin on N-alpha-tosyl L-arginine methyl ester [TAME]-esterase induced contractions on rat aorta in vitro

The present study was designed to investigate whether N-alpha-tosyl L-arginine methyl ester [TAME]-esterase activation could be the result of endothelial dysfunction. Thoracic aorta from rats was mounted in an organ bath containing Krebs solution. Intact and endothelium denuded aortic strips were challenged with different concentrations of TAME (10(-15)-10(-1) m). The effects of aspirin, a cyclo-oxygenase pathway inhibitor, were also studied on [TAME]-esterase induced contraction on rat aorta strips. Our results showed that aspirin definitely blocked TAME-esterase induced contractions on rat aortic strips. In conclusion, the present work supported the hypothesis that [TAME]-esterase induced contraction in rat aorta in vitro was mediated through release of prostaglandin(s) as a result of endothelial dysfunction.

Sevoflurane and bradykinin-induced calcium mobilization in pulmonary arterial valvular endothelial cells in situ: sevoflurane stimulates plasmalemmal calcium influx into endothelial cells

Kinins locally synthesized in the cardiovascular tissue are believed to contribute to the regulation of cardiovascular homeostasis by stimulating the endothelial cells to release nitric oxide, prostacyclin, or a hyperpolarizing factor via autocrine-paracrine mechanisms. This study was designed to investigate the action of sevoflurane on bradykinin-induced Ca2+ mobilization in endothelial cells in situ. Utilizing fura-2-loaded rat pulmonary arterial valve leaflets, the effects of sevoflurane were examined on bradykinin-induced increases in intracellular Ca2+ concentration ([Ca2+]i) in endothelial cells in situ. In the presence of extracellular Ca2+ (1.5 mM), bradykinin (3-30 microM) produced an initial phasic and a subsequent tonic increase in [Ca2+]i in a concentration-dependent manner. However, it produced only the phasic increase in [Ca2+]i in the absence of extracellular Ca2+. Sevoflurane (5%, 0.67 mM) inhibited both the phasic and tonic responses to bradykinin. In these experiments, sevoflurane (3-5%) generated sustained increases (approximately 20-40% of the bradykinin-induced maximal increase in [Ca2+]i) in the resting [Ca2+]i level. Sevoflurane still increased [Ca2+]i after depletion of the intracellular Ca stores with ionomycin (0.1 microM ). However, the sevoflurane-induced increase in [Ca2+]i was eliminated by removal of the extracellular Ca and attenuated by NiCl (1-3 mM). In conclusion, in the pulmonary arterial valvular endothelial cells, sevoflurane inhibits both bradykinin-induced Ca2+ release from the intracellular stores and bradykinin-induced plasmalemmal Ca2+ influx. In addition, sevoflurane appears to stimulate the plasmalemmal Ca2+ influx and thereby increase the endothelial [Ca2+]i level. Sevoflurane might influence the pulmonary vascular tone through its direct action on the pulmonary arterial valvular endothelial cells.

Multiple interactions between the renin-angiotensin and the kallikrein-kinin systems: role of ACE inhibition and AT1 receptor blockade

The investigation of therapeutic actions of angiotensin type 1 (AT1) receptor antagonists and ACE inhibitors (ACEI) demonstrated complex interactions between the renin-angiotensin system (RAS) and the kallikrein-kinin system (KKS) in several experimental and clinical studies. They are evidenced by the fact that (1) ACE efficiently catabolizes kinins; (2) angiotensin-derivatives such as ANG-(1-7) exert kininlike effects; and (3) kallikrein probably serves as a prorenin-activating enzyme. (4) Several authors have demonstrated experimentally that the protective effects of ACEI are at least partly mediated by a direct potentiation of kinin receptor response on BK stimulation. (5) Furthermore, studies on AT1 antagonists, which do not directly influence kinin degradation, and studies on angiotensin-receptor transgenic mice have revealed additional interactions between the RAS and the KKS. There is mounting evidence that an autocrine cascade including kinins, nitric oxide, prostaglandins, and cyclic GMP is involved in at least some of the angiotensin type 2 receptor effects. This review discusses multiple possibilities of cross-talks between the RAS and KKS in vascular and cardiac physiology and pathology after ACE inhibition and AT1 receptor blockade.

Apstatin, a selective inhibitor of aminopeptidase P, reduces myocardial infarct size by a kinin-dependent pathway

1. Inhibitors of the angiotensin converting enzyme (ACE) have been shown to exert their cardioprotective actions through a kinin-dependent mechanism. ACE is not the only kinin degrading enzyme in the rat heart. 2. Since aminopeptidase P (APP) has been shown to participate in myocardial kinin metabolism to the same extent as ACE, the aims of the present study were to investigate whether (a) inhibition of APP leads to a reduction of myocardial infarct size in a rat model of acute ischaemia and reperfusion, (b) reduction of infarct size is mediated by bradykinin, and (c) a combination of APP and ACE inhibition leads to a more pronounced effect than APP inhibition alone. 3. Pentobarbital-anaesthetized rats were subjected to 30 min left coronary artery occlusion followed by 3 h reperfusion. The APP inhibitor apstatin, the ACE-inhibitor ramiprilat, or their combination were administered 5 min before ischaemia. Rats receiving HOE140, a specific B(2) receptor antagonist, were pretreated 5 min prior to enzyme inhibitors. Myocardial infarct size (IS) was determined by tetrazolium staining and expressed as percentage of the area at risk (AAR). 4. IS/AAR% was significantly reduced in rats that received apstatin (18+/-2%), ramiprilat (18+/-3%), or apstatin plus ramiprilat (20+/-4%) as compared with those receiving saline (40+/-2%), HOE (43+/-3%) or apstatin plus HOE140 (49+/-4%). 5. Apstatin reduces IS in an in vivo model of acute myocardial ischaemia and reperfusion to the same extent than ramiprilat. Cardioprotection achieved by this selective inhibitor of APP is mediated by bradykinin. Combined inhibition of APP and ACE did not result in a more pronounced reduction of IS than APP-inhibition alone.

Pathways of bradykinin degradation in blood and plasma of normotensive and hypertensive rats

Kinins are vasoactive peptide hormones that can confer protection against the development of hypertension. Because their efficacy is greatly influenced by the rate of enzymatic degradation, the activities of various kininases in plasma and blood of spontaneously hypertensive rats (SHR) were compared with those in normotensive Wistar-Kyoto rats (WKY) to identify pathogenic alterations. Either plasma or whole blood was incubated with bradykinin (10 microM). Bradykinin and kinin metabolites were measured by high-performance liquid chromatography. Kininase activities were determined by cumulative inhibition of angiotensin I-converting enzyme (ACE), carboxypeptidase N (CPN), and aminopeptidase P (APP), using selective inhibitors. Plasma of WKY rats degraded bradykinin at a rate of 13.3 +/- 0.94 micromol x min(-1) x l(-1). The enzymes ACE, APP, and CPN represented 92% of this kininase activity, with relative contributions of 52, 25, and 16%, respectively. Inclusion of blood cells at physiological concentrations did not extend the activities of these plasma kininases further. No differences of kinin degradation were found between WKY and SHR. The identical conditions of kinin degradation in WKY and SHR suggest no pathogenic role of kininases in the SHR model of genetic hypertension.

Non-competitive pharmacological antagonism at the rabbit B(1) receptor

The B(1) receptor for kinins, stimulated by kinin metabolites without the C-terminal Arg residue (e.g., des-Arg(9)-bradykinin (BK) and Lys-des-Arg(9)-BK), is an increasingly recognized molecular target for the development of analgesic and anti-inflammatory drugs. Recently developed antagonists of this receptor were compared to a conventional antagonist, Ac-Lys-[Leu(8)]-des-Arg(9)-BK, in pharmacological assays based on the rabbit B(1) receptor. B-9858 (Lys-Lys-[Hyp(3), Igl(5), D-Igl(7), Oic(8)]des-Arg(9)-BK) and three other analogues possessing the alpha-2-indanylglycine(5) (Igl(5)) residue (order of potency B-9858 approximately B-10146>B-10148>B-10050) were partially insurmountable antagonists of des-Arg(9)-BK in the contractility assay based on rabbit aortic rings. B-9858-induced depression of the maximal effect was more pronounced in tissues treated with the protein synthesis inhibitor cycloheximide to block the spontaneous increase of response attributed to the post-isolation formation of B(1) receptors, and only partly reversible on washing. By comparison, Ac-Lys-[Leu(8)]des-Arg(9)-BK was a surmountable antagonist (pA(2) 7. 5), even in cycloheximide-treated tissues. B-9958 (Lys-[Hyp(3), CpG(5), D-Tic(7), CpG(8)]des-Arg(9)-BK) was also surmountable (pA(2) 8.5). The binding of [(3)H]-Lys-des-Arg(9)-BK to recombinant rabbit B(1) receptors expressed in COS-1 cells was influenced by two of the antagonists: while Ac-Lys-[Leu(8)]des-Arg(9)-BK competed for the radioligand binding without affecting the B(max), B-9858 decreased the B(max) in a time-dependent and washout-resistant manner. B-9858 and analogues possessing Igl(5) are the first reported non-competitive, non-equilibrium antagonists of the kinin B(1) receptor.

Reduced cardiac hypertrophy and altered blood pressure control in transgenic rats with the human tissue kallikrein gene

To evaluate the cardiovascular actions of kinins, we established a transgenic rat line harboring the human tissue kallikrein gene, TGR(hKLK1). Under the control of the zinc-inducible metallothionein promoter, the transgene was expressed in most tissues including the heart, kidney, lung, and brain, and human kallikrein was detected in the urine of transgenic animals. Transgenic rats had a lower 24-h mean arterial pressure in comparison with control rats, which was further decreased when their diet was supplemented with zinc. The day/night rhythm of blood pressure was significantly diminished in TGR(hKLK1) animals, whereas the circadian rhythms of heart rate and locomotor activity were unaffected. Induction of cardiac hypertrophy by isoproterenol treatment revealed a marked protective effect of the kallikrein transgene because the cardiac weight of TGR(hKLK1) increased significantly less, and the expression of atrial natriuretic peptide and collagen III as markers for hypertrophy and fibrosis, respectively, were less enhanced. The specific kinin-B2 receptor antagonist, icatibant, abolished this cardioprotective effect. In conclusion, the kallikrein-kinin system is an important determinant in the regulation of blood pressure and its circadian rhythmicity. It also exerts antihypertrophic and antifibrotic actions in the heart.