A nonpeptide mimic of bradykinin blunts the development of hypertension in young spontaneously hypertensive rats

Novel Insights into the Kallikrein-Kinin System in Fulminant Myocarditis: Physiological Basis and Potential Therapeutic Advances

Fulminant myocarditis (FM) is characterized by rapid cardiac deterioration often instigated by an inflammatory cytokine storm. The kallikrein-kinin system (KKS) is a metabolic cascade known for releasing vasoactive kinins, such as bradykinin-related peptides, possessing diverse pharmacological activities that include inflammation, regulation of vascular permeability, endothelial barrier dysfunction, and blood pressure modulation. The type 1 and type 2 bradykinin receptors (B1R and B2R), integral components of the KKS system, mediate the primary biological effects of kinin peptides. This review aims to offer a comprehensive overview of the primary mechanisms of the KKS in FM, including an examination of the structural components, regulatory activation, and downstream signaling pathways of the KKS. Furthermore, it explores the involvement of the tissue kallikrein/B1R/inducible nitric oxide synthase (TK/B1R/iNOS) pathway in myocyte dysfunction, modulation of the immune response, and preservation of endothelial barrier integrity. The potential therapeutic advances targeting the inhibition of the KKS in managing FM will be discussed, providing valuable insights for the development of clinical treatment strategies.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

Effects of inactivation-resistant agonists on the signalling, desensitization and down-regulation of bradykinin B(2) receptors

BACKGROUND AND PURPOSE

A peptide bradykinin (BK) B(2) receptor agonist partially resistant to degradation, B-9972, down-regulates this receptor subtype. We have used another recently described non-peptide agonist, compound 47a, as a tool to study further the effects of metabolically more stable and thus persistent, agonists of the BK B(2) receptor on signalling, desensitization and down-regulation of this receptor.

EXPERIMENTAL APPROACH AND KEY RESULTS

Compound 47a was a partial agonist at the B(2) receptor in the human umbilical vein, where it shared with B-9972 a very slow relaxation on washout, and in HEK 293 cell lines expressing tagged forms [myc, green fluorescent protein (GFP)] of the rabbit B(2) receptor. Compound 47a desensitized the umbilical vein to BK. In the cellular systems, the inactivation-resistant agonists induced [Ca(2+)](i) transients as brief as those of BK but affected other functions with a longer duration than BK [12 h; receptor endocytosis, endosomal beta-arrestin(1/2) translocation, protein kinase C-dependent extracellular signal-regulated kinases (ERK)1/2 phosphorylation and c-Fos expression]. The B(2) receptor-GFP was degraded in cells exposed to B-9972 or compound 47a for 12 h. The non-peptide B(2) receptor antagonist LF 16-0687 prevented all effects of compound 47a, which were also absent in cells lacking recombinant B(2) receptors.

CONCLUSION AND IMPLICATIONS

Inactivation-resistant agonists revealed a long-lasting assembly of the agonist-B(2) receptor-beta-arrestin complexes in endosomal structures and induce 'biased signalling' (in terms of activation of ERK and c-Fos) as a function of time. Further, B-9972 and compound 47a, unlike BK, efficiently down-regulated BK B(2) receptors.

NaCl plus chitosan as a dietary salt to prevent the development of hypertension in spontaneously hypertensive rats

The effect of NaCl plus 3% chitosan on the systolic blood pressure of spontaneously hypertensive rats (SHR) were evaluated and compared with NaCl plus KCl (NaCl, 49.36% + KCl 49.36%) and chitosan or NaCl treatment alone. In SHR, administration of NaCl plus chitosan (44 mM Na/day) for two months significantly decreased the systolic blood pressure greater than of NaCl plus KCl and NaCl alone. NaCl plus chitosan resulted, though not statistically significant, in decreased urinary Na⁺ excretion and decreased blood urea nitrogen levels. Urinary creatinine of NaCl plus chitosan was slightly decreased compared to 3 treated groups. Serum electrolytes levels, however, remained unchanged. The combination of NaCl and chitosan may be superior to the conventional use of NaCl plus KCl or NaCl alone in the prevention of hypertension. Even though these supplementary diets have demonstrated potential anti-hypertensive effects in the experimental animal model, further research is needed before any recommendations can be made.

Structure-activity relationships of novel peptide agonists of the human bradykinin B2 receptor

The nonapeptide bradykinin (BK) is involved in the genesis of inflammation, edema and in pain mediation. As such, much effort has gone into the development of peptide/non-peptide antagonists to counteract these processes. However, there is an increasing awareness of the potential value of chemically stable BK agonists in the treatment of diabetes and cardiovascular diseases. In this study, a structure-activity relationship study of BK was performed to develop potent and stable peptide mimetics active at the human B2 receptors (hB2R). Twenty-three analogues were produced with substitutions at positions 1, 3, 5, 7, 8 and/or 9 of BK. In vitro binding (on transiently transfected HEK-293T cells) and biological activities (vasomotricity tests on human umbilical veins, MAPK assays on HEK-293T cells) of novel BK peptide derivatives at hB2R were determined alongside with previously reported synthetic agonists (e.g. RMP-7, JMV1609, FR190997). Some peptides were also tested in vivo in rats and rabbits using blood pressure assays. Two compounds, [Hyp(3), Thi(5), Cha(8)]-BK and [Hyp(3), Thi(5), (N)Chg(7), Thi(8)]-BK, exhibited equivalent (or even greater) in vitro affinities and potencies to BK at the naturally expressed and recombinant hB2R. Their potency and duration of action in vivo were highly superior to BK, thus inferring that they can withstand intravascular proteolysis. These novel compounds show promise as candidates for investigating the pharmacology of BK receptors and developing potential therapeutical applications.

The kallikrein-kinin system: current and future pharmacological targets

The kallikrein-kinin system is an endogenous metabolic cascade, triggering of which results in the release of vasoactive kinins (bradykinin-related peptides). This complex system includes the precursors of kinins known as kininogens and mainly tissue and plasma kallikreins. The pharmacologically active kinins, which are often considered as either proinflammatory or cardioprotective, are implicated in many physiological and pathological processes. The interest of the various components of this multi-protein system is explained in part by the multiplicity of its pharmacological activities, mediated not only by kinins and their receptors, but also by their precursors and their activators and the metallopeptidases and the antiproteases that limit their activities. The regulation of this system by serpins and the wide distribution of the different constituents add to the complexity of this system, as well as its multiple relationships with other important metabolic pathways such as the renin-angiotensin, coagulation, or complement pathways. The purpose of this review is to summarize the main properties of this kallikrein-kinin system and to address the multiple pharmacological interventions that modulate the functions of this system, restraining its proinflammatory effects or potentiating its cardiovascular properties.

Effect of prepuberal gonadectomy upon aldosterone levels in female and male SHR: interaction between blood pressure and kallikrein kinin system

It has been suggested that an abnormal activity of the hypothalamic-pituitary-adrenal-gonadal axis may be implicated in the pathogenesis of spontaneously hypertensive rats (SHR) blood pressure hypertension. However, it is widely known that the kallikrein-kinin system plays a role in blood pressure regulation in this strain, because an inverse relation between blood pressure and urinary kallikrein excretion has been reported. It was of our interest to study how early suppression of sexual hormones affected blood pressure regulation in SHR and urinary kallikrein excretion and to elucidate the involved mechanisms. For these purpose, SH and Wistar-Kyoto (WKY) rats blood pressure, renal function, and hormonal profile were studied after prepuberal gonadectomy starting at 4 weeks of age throughout until the 12th week of age. Results were compared with those of untreated SH and WKY rats of either sex. The response to blocking agents against aldosterone and kallikrein-kinin system also were evaluated. Systolic blood pressure increased progressively in male and female SHR 12 weeks of age. Systolic blood pressure was higher in male than in female SHR, but urinary kallikrein was lower in male SHR. Prepuberal gonadectomy induced a significant decrease in systolic blood pressure in male and in female SHR at 12 weeks of age, accompanied by an increase in urinary kallikrein in male and in female SHR. Plasma aldosterone increased markedly in female and male SHR after gonadectomy. No concurrent changes in plasma renin activity or corticosterone levels were observed. The aldosterone receptor antagonist and the kallikrein inhibitor treatment blunted the blood pressure lowering effect of gonadectomy and diminished urinary kallikrein excretion. Results support the existence of a sexual dimorphism related to hypertension and urinary kallikrein and suggest an interaction among the kallikrein-kinin system, sexual hormones, and mineralocorticoids in the neonatal programming of hypertension.

Discovery of the First Non-Peptide Full Agonists for the Human Bradykinin B2 Receptor Incorporating 4-(2-Picolyloxy)quinoline and 1-(2-Picolyl)benzimidazole Frameworks

In the course of our studies on non-peptide bradykinin (BK) B(2) receptor ligands, it was suggested that the 4-substituent of the quinoline ring may play a critical role in determining binding affinities for human and guinea pig B(2) receptors, as well as agonist/antagonist properties. We carried out an extensive investigation to elucidate the structure-activity relationships (SAR) for this key pharmacophore. Introduction of lower alkoxy groups to the 4-position of the quinoline ring of 3 led to the identification of 4-ethoxy derivative 22b as a unique partial agonist. This compound significantly stimulated inositol phosphates (IPs) formation in Chinese hamster ovary cells expressing the cloned human B(2) receptor at concentrations greater than 10 nM and displayed one-tenth of the intrinsic activity of BK. The agonist activity of 22b was selective for the B(2) receptor and was inhibited by selective peptide and non-peptide B(2) antagonists. On the other hand, 22b strongly suppressed BK-induced IPs formation through the cloned human B(2) receptor. Further studies on the key pharmacophore led to identification of a 2-picolyloxy moiety as a powerful agonist switch, leading to the discovery of a potent and efficacious non-peptide B(2) agonist, 19a. Successive optimization of the acyl side chain afforded 38, which exhibited full agonist activity on stimulation of IPs formation. Furthermore, this strategy could be applied successfully to the benzimidazole series. The representative 1-(2-picolyl)benzimidazole derivative 47c increased PGE(2) production at a 1 microM concentration to the same level as the maximum effect of BK. Thus, we have established the medicinal chemistry modifications required to convert our highly potent non-peptide B(2) antagonists to agonists with potent efficacy.

The therapeutic potential of bradykinin B2 receptor agonists in the treatment of cardiovascular disease

The nonapeptide bradykinin (BK) is a Janus-faced hormone, which exerts pathophysiological as well as pronounced beneficial physiological effects, mainly by stimulation of BK B(2) receptors. In various animal models and in humans it has been shown that the stimulation of BK B(2) receptors is not only implicated in the pathogenesis of inflammation, pain and tissue injury but also in powerful cardioprotective mechanisms. Either exogenous administration of BK or locally increased BK concentrations as a consequence of the inhibition of its metabolic breakdown by angiotensin-converting enzyme inhibitors, reveal the significant contribution of BK in powerful cardioprotective mechanisms. These are mainly triggered by the synthesis and release of the vasorelaxant, anti-hypertrophic and anti-atherosclerotic endothelial mediators nitric oxide, prostaglandins and tissue-type plasminogen activator, by ischaemic preconditioning and by an increase in insulin sensitivity. Consequently, BK B(2) receptor agonists may have important clinical value in the treatment and prevention of various cardiovascular disorders such as hypertension, ischaemic heart disease, left ventricular hypertrophy, ventricular remodelling and congestive heart failure as well as diabetic disorders by mimicking the reported beneficial effects of BK. However, none of the currently known potent and selective peptide and non-peptide agonists of BK B(2) receptors--RMP-7 (lobradamil, Cereport; Alkermes), JMV-1116 (Fournier), FR-190997 (Fujisawa) and FR-191413 (Fujisawa)--have been selected for a clinical assessment in cardiovascular indications. One major challenge of this approach is the still unanswered question of whether there is a sufficient safe therapeutic window between potential cardioprotective and pro-inflammatory effects following BK B(2) receptor agonism.

Bradykinin inhibits development of myocardial infarction through B2 receptor signalling by increment of regional blood flow around the ischaemic lesions in rats

1 To identify the roles of endogenous kinins in prevention of myocardial infarction (MI), we performed the permanent ligation of coronary artery in rats. 2 The size of MI 12, 24, and 48 h after coronary ligation in kininogen-deficient Brown Norway Katholiek (BN-Ka) rats was significantly larger (49.7+/-0.2%, 49.6+/-2%, and 51.1+/-1%, respectively) than that of kinin-replete Brown Norway Kitasato (BN-Ki) rats (42+/-2%, 38.5+/-4%, and 41.5+/-1%). 3 Hoe140, a bradykinin (BK) B(2) receptor antagonist injected (1.0 mg kg(-1), i.v.) half an hour before, and every 8 h after, coronary ligation, significantly increased the size of MI in Sprague-Dawley rats. Aprotinin, a kallikrein inhibitor, which was infused intravenously (10,000 Units kg(-1) h(-1)) with an osmotic mini-pump, significantly increased the size of an MI 24 h after ligation. 4 When evaluated using microspheres, the regional myocardial blood flow around the necrotic lesion in BN-Ka rats 6 h after ligation was reduced more than that in BN-Ki rats with MI by 41-46%. The same was true in Hoe140-treated BN-Ki rats. 5 FR190997, a nonpeptide B(2) agonist, which was infused (10 microg kg(-1) h(-1)) into the vena cava of BN-Ka rats for 24 h with an osmotic mini-pump, caused significant reduction in the size of MI (38+/-3%), in comparison with the size in vehicle solution-treated rats (51+/-3%). The size of MI in FR190997-treated BN-Ka rats was the same as in BN-Ki rats. 6 These results suggested that endogenous kinin has the capacity to reduce the size of MI via B(2) receptor signalling because of the increase in regional myocardial blood flow around the ischaemic lesion.

Potassium-induced increase in renal kallikrein secretion is attenuated in dissected renal connecting tubules of young spontaneously hypertensive rats

It is suggested that attenuation of the renal kallikrein-kinin system (KKS) involved the development of hypertension in young spontaneously hypertensive rats (SHR). In the present study, a comparison was made between young SHR and Wistar Kyoto rats (WKY) to examine the ability to secrete renal kallikrein from the microdissected connecting tubules (CNT) by potassium or an ATP-sensitive potassium channel blocker, 4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexylhydrochloride (PNU-37883A), both of which are renal kallikrein secretagogues. Maximum effect of potassium on kallikrein secretion was observed 10 min after placing the tubules at concentration of 20 mM. Kallikrein secretion was also increased concentration-dependently by PNU-37883A (0.1, 1, 10, and 100 microM). In the presence of EDTA, NiCl2, verapamil, xestspongin C (an inositol 1,4,5-trisphosphate (IP3) receptor-selective antagonist), or ruthenium red (a ryanodine-sensitive receptor blocker), potassium-induced increase in renal kallikrein secretion was inhibited. Augmentation of renal kallikrein secretion by potassium or PNU-37883A was diminished in SHR compared to WKY. These results indicate that the ability to secrete renal kallikrein by potassium was attenuated in young SHR compared with WKY. Furthermore, it is suggested that the potassium-induced renal kallikrein secretion requires an extracellular Ca2+ entry through Ca2+ channels including L-type Ca2+ channels and Ca2+ release from intracellular Ca2+ stores through IP3 receptor and ryanodine receptor.

Proinflammatory characteristics of a nonpeptide bradykinin mimic, FR190997, in vivo

1. Proinflammatory potency of the nonpeptide bradykinin (BK) B(2) receptor agonist FR190997 (8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl)cinnamidoacetyl]-N-methylamino]benzyloxy]-2-methyl-4-(2-pyridylmethoxy)quinoline) was investigated. 2. Intradermal injection of FR190997 (0.03 - 3 nmol site(-1)) into dorsal skin of rats increased vascular permeability in a dose-dependent manner. The effect was less than that of BK, but it was long-acting and was inhibited by treatment with FR173657 (3 mg kg(-1), p.o.). Captopril (10 mg kg(-1), i.p.) did not enhance the plasma extravasation by FR190997 (0.3 nmol site(-1)) in the presence of soybean trypsin inhibitor (SBTI, 30 microg site(-1)). 3. Subcutaneous injection of FR190997 (3 nmol site(-1)) into the hindpaw of mice markedly induced paw swelling. The oedema lasted up to 3 h after the injection. Administration of indomethacin or NS-398 (10 mg kg(-1), i.p.) significantly reduced it at 3 h after the injection. 4. Simultaneous i.p. injection of prostaglandin (PG) E(2) (1 nmol site(-1)) or beraprost sodium (0.5 nmol site(-1)) with FR190997 (5 nmol site(-1)) greatly enhanced frequency of writhing reactions in mice. 5. FR190997 (0.3 - 30 nmol kg(-1), i.v.) showed less increase in airway opening pressure (Pao) in the guinea-pig after i.v. injection. Furthermore, FR190997 (0.03 - 30 nmol) resulted in a very weak contraction of tracheal ring strips and lung parenchymal sections in vitro. 6. In mice sponge implants, topical application of FR190997 increased angiogenesis and granulation with enhanced expressions of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) mRNAs. 7. These results indicate that FR190997 has proinflammatory long-lasting characteristics and it might be 'a stable tool' for studying the role of BK B(2) receptor in vivo.

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.