Molecular biology of the kallikrein-kinin system: from structure to function

Soluble CD13 induces inflammatory arthritis by activating the bradykinin receptor B1

CD13, an ectoenzyme on myeloid and stromal cells, also circulates as a shed, soluble protein (sCD13) with powerful chemoattractant, angiogenic, and arthritogenic properties, which require engagement of a G protein-coupled receptor (GPCR). Here we identify the GPCR that mediates sCD13 arthritogenic actions as the bradykinin receptor B1 (B1R). Immunofluorescence and immunoblotting verified high expression of B1R in rheumatoid arthritis (RA) synovial tissue and fibroblast-like synoviocytes (FLSs), and demonstrated binding of sCD13 to B1R. Chemotaxis, and phosphorylation of Erk1/2, induced by sCD13, were inhibited by B1R antagonists. In ex vivo RA synovial tissue organ cultures, a B1R antagonist reduced secretion of inflammatory cytokines. Several mouse arthritis models, including serum transfer, antigen-induced, and local innate immune stimulation arthritis models, were attenuated in Cd13-/- and B1R-/- mice and were alleviated by B1R antagonism. These results establish a CD13/B1R axis in the pathogenesis of inflammatory arthritis and identify B1R as a compelling therapeutic target in RA and potentially other inflammatory diseases.

Polymorphism of the bradykinin type 2 receptor gene modulates blood pressure profile and microvascular function in prepubescent children

Previous reports reveal that +9/-9 polymorphism of the bradykinin B2 receptor (BDKRB2) is suggestive of cardiometabolic diseases. The aim of this study was to examine the impact of BDKRB2 + 9/-9 polymorphism genotypes on the blood pressure parameters and microvascular function in prepubescent children. We screened for BDKRB2 + 9/-9 polymorphism in the DNA of 145 children (86 boys and 59 girls), and its association with body composition, blood pressure levels, biochemical parameters, and endothelial function was determined. No significant association of the BDKRB2 genotypes with gender (P=0.377), race (P=0.949) or family history of cardiovascular disease (CVD) (P=0.858) was observed. Moreover, we did not identify any interaction between BDKRB2 genotypes with a phenotype of obesity (P=0.144). Children carrying the +9/+9 genotype exhibited a significant linear trend with higher levels of systolic blood pressure and pulse pressure (P<0.001). Moreover, the presence of +9 allele resulted in a decrease of reactive hyperemia index, showing a decreasing linear trend from -9/-9 to +9/+9, wherein this parameter of endothelial function was the lowest in the +9/+9 children, intermediate in the +9/-9 children, and the highest in the -9/-9 children (P<0.001). There was a significant inverse correlation between reactive hyperemia index and systolic blood pressure (r= - 0.348, P< 0.001) and pulse pressure (r= - 0.399, P< 0.001). Our findings indicate that the +9/+9 BDKRB2 genotype was associated with high blood pressure and microvascular dysfunction in prepubescent Brazilian children.

Contact System Activation in Plasma from Dengue Patients Might Harness Endothelial Virus Replication through the Signaling of Bradykinin Receptors

Since exacerbated inflammation and microvascular leakage are hallmarks of dengue virus (DENV) infection, here we interrogated whether systemic activation of the contact/kallikrein-kinin system (KKS) might hamper endothelial function. In vitro assays showed that dextran sulfate, a potent contact activator, failed to generate appreciable levels of activated plasma kallikrein (PKa) in the large majority of samples from a dengue cohort (n = 70), irrespective of severity of clinical symptoms. Impaired formation of PKa in dengue-plasmas correlated with the presence of cleaved Factor XII and high molecular weight kininogen (HK), suggesting that the prothrombogenic contact system is frequently triggered during the course of infection. Using two pathogenic arboviruses, DENV or Zika virus (ZIKV), we then asked whether exogenous BK could influence the outcome of infection of human brain microvascular endothelial cells (HBMECs). Unlike the unresponsive phenotype of Zika-infected HBMECs, we found that BK, acting via B2R, vigorously stimulated DENV-2 replication by reverting nitric oxide-driven apoptosis of endothelial cells. Using the mouse model of cerebral dengue infection, we next demonstrated that B2R targeting by icatibant decreased viral load in brain tissues. In summary, our study suggests that contact/KKS activation followed by BK-induced enhancement of DENV replication in the endothelium may underlie microvascular pathology in dengue.

Kinin B1 receptors as a therapeutic target for inflammation

INTRODUCTION

Kinins are peptide mediators exerting their pro-inflammatory actions by the selective stimulation of two distinct G-protein coupled receptors, termed BKB1R and BKB2R. While BKB2R is constitutively expressed in a multitude of tissues, BKB1R is hardly expressed at baseline but highly inducible by inflammatory mediators. In particular, BKB1R was shown to be involved in the pathogenesis of numerous inflammatory diseases. Areas covered: This review intends to evaluate the therapeutic potential of substances interacting with the BKB1R. To this purpose we summarize the published literature on animal studies with antagonists and knockout mice for this receptor. Expert Opinion: In most cases the pharmacological inhibition of BKB1R or its genetic deletion was beneficial for the outcome of the disease in animal models. Therefore, several companies have developed BKB1R antagonists and tested them in phase I and II clinical trials. However, none of the developed BKB1R antagonists was further developed for clinical use. We discuss possible reasons for this failure of translation of preclinical findings on BKB1R antagonists into the clinic.

Kinin-B1 and B2 receptor activity in proliferation and neural phenotype determination of mouse embryonic stem cells

The kinins bradykinin and des-arg(9) -bradykinin cleaved from kininogen precursors by kallikreins exert their biological actions by stimulating kinin-B2 and B1 receptors, respectively. In vitro models of neural differentiation such as P19 embryonal carcinoma cells and neural progenitor cells have suggested the involvement of B2 receptors in neural differentiation and phenotype determination; however, the involvement of B1 receptors in these processes has not been established. Here, we show that B1 and B2 receptors are differentially expressed in mouse embryonic E14Tg2A stem cells undergoing neural differentiation. Proliferation and differentiation assays, performed in the presence of receptor subtype-selective agonists and antagonists, revealed that B1 receptor activity is required for the proliferation of embryonic and differentiating cells as well as for neuronal maturation at later stages of differentiation, while the B2 receptor acts on neural phenotype choice, promoting neurogenesis over gliogenesis. Besides the elucidation of bradykinin functions in an in vitro model reflecting early embryogenesis and neurogenesis, this study contributes to the understanding of B1 receptor functions in this process.

Analysis of erectile responses to bradykinin in the anesthetized rat

The kallikrein-kinin system is expressed in the corpus cavernosa, and bradykinin (BK) relaxes isolated corpora cavernosal strips. However, erectile responses to BK in the rat have not been investigated in vivo. In the present study, responses to intracorporal (ic) injections of BK were investigated in the anesthetized rat. BK, in doses of 1-100 μg/kg ic, produced dose-related increases in intracavernosal pressure (ICP) and dose-related deceases in mean arterial pressure (MAP). When decreases in MAP were prevented by intravenous injections of angiotensin II (Ang II), increases in ICP, in response to BK, were enhanced. Increases in ICP, ICP/MAP ratio, and area under the curve and decreases in MAP in response to BK were inhibited by the kinin B2 receptor antagonist HOE-140 and enhanced by the angiotensin-converting enzyme (ACE) inhibitor captopril and by Ang-(1-7). Increases in ICP, in response to BK, were not attenuated by the nitric oxide (NO) synthase inhibitor (N(ω)-nitro-L-arginine methyl ester) or the soluble guanylate cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) but were attenuated by the cyclooxygenase inhibitor, sodium meclofenamate. Decreases in MAP were not attenuated by either inhibitor. These data suggest that erectile responses are mediated by kinin B2 receptors and modulated by decreases in MAP. These data indicate that ACE is important in the inactivation of BK and that erectile and hypotensive responses are independent of NO in the penis or the systemic vascular bed. Erectile responses to cavernosal nerve stimulation are not altered by BK or HOE-140, suggesting that BK and B2 receptors do not modulate nerve-mediated erectile responses under physiologic conditions. These data suggest that erectile responses to BK are mediated, in part, by the release of cyclooxygenase products.

What have we learned about the kallikrein-kinin and renin-angiotensin systems in neurological disorders?

The kallikrein-kinin system (KKS) is an intricate endogenous pathway involved in several physiological and pathological cascades in the brain. Due to the pathological effects of kinins in blood vessels and tissues, their formation and degradation are tightly controlled. Their components have been related to several central nervous system diseases such as stroke, Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, epilepsy and others. Bradykinin and its receptors (B1R and B2R) may have a role in the pathophysiology of certain central nervous system diseases. It has been suggested that kinin B1R is up-regulated in pathological conditions and has a neurodegenerative pattern, while kinin B2R is constitutive and can act as a neuroprotective factor in many neurological conditions. The renin angiotensin system (RAS) is an important blood pressure regulator and controls both sodium and water intake. AngII is a potent vasoconstrictor molecule and angiotensin converting enzyme is the major enzyme responsible for its release. AngII acts mainly on the AT1 receptor, with involvement in several systemic and neurological disorders. Brain RAS has been associated with physiological pathways, but is also associated with brain disorders. This review describes topics relating to the involvement of both systems in several forms of brain dysfunction and indicates components of the KKS and RAS that have been used as targets in several pharmacological approaches.

Altered glucose homeostasis and hepatic function in obese mice deficient for both kinin receptor genes

The Kallikrein-Kinin System (KKS) has been implicated in several aspects of metabolism, including the regulation of glucose homeostasis and adiposity. Kinins and des-Arg-kinins are the major effectors of this system and promote their effects by binding to two different receptors, the kinin B2 and B1 receptors, respectively. To understand the influence of the KKS on the pathophysiology of obesity and type 2 diabetes (T2DM), we generated an animal model deficient for both kinin receptor genes and leptin (obB1B2KO). Six-month-old obB1B2KO mice showed increased blood glucose levels. Isolated islets of the transgenic animals were more responsive to glucose stimulation releasing greater amounts of insulin, mainly in 3-month-old mice, which was corroborated by elevated serum C-peptide concentrations. Furthermore, they presented hepatomegaly, pronounced steatosis, and increased levels of circulating transaminases. This mouse also demonstrated exacerbated gluconeogenesis during the pyruvate challenge test. The hepatic abnormalities were accompanied by changes in the gene expression of factors linked to glucose and lipid metabolisms in the liver. Thus, we conclude that kinin receptors are important for modulation of insulin secretion and for the preservation of normal glucose levels and hepatic functions in obese mice, suggesting a protective role of the KKS regarding complications associated with obesity and T2DM.

Age-related changes in kallikreins-kinins system in rat corpus cavernosum

Many factors, such as nitric oxide synthase, androgen and growth factors, can regulate the tone of corpus cavernosum (CC) smooth muscle with an age-related tendency. It has been shown that the active metabolites of kallikreins-kinins system (KKS), including bradykinin, Lys-BK and Met-Lys-BK, can also relax the CC smooth muscle significantly in vitro. Our aim was to evaluate the specific association between KKS and age in rat CC. CC and thoracic aorta were isolated from rats at postnatal weeks (PW) of 2, 8, 12, 20, 30, 40 and 60, respectively. Tissue kallikrein-I (KLKI) and kinin B2 receptor (B2R) mRNA in CC and thoracic aorta were detected by real-time polymerase chain reaction (PCR). Protein expression of KLKI and B2R were determined with immunofluorescence in situ and Western blot. Real-time PCR, immunofluorescence in situ and Western blot all demonstrated that the age-related changes in expression of KLKI were similar between the CC and thoracic aorta. It significantly increased with age from PW2 to PW30, reached the peak at PW30 and then declined gradually. However, there was no statistically significant difference among PW30, PW40 and PW60. Similarly, the expression of B2R increased gradually with age reached and remained at the peak during adult stages and no significant differences were found among PW20, PW30 and PW40; then, it decreased significantly at PW60. The changes in the expression of B2R in CC and age-matched aorta were similar except that it was significantly less than that in the aorta at PW60. The expression of KLKI and B2R changed in an age-dependent pattern in rat CC and have a tendency to decline during ageing, which is of the same tendency as reported for erection capacity in ageing males and suggests why ageing is an independent predictor of ED, to some extent.

Heparin modulation of human plasma kallikrein on different substrates and inhibitors

The interplay of different proteases and glycosaminoglycans is able to modulate the activity of the enzymes and to affect their structures. Human plasma kallikrein (huPK) is a proteolytic enzyme involved in intrinsic blood clotting, the kallikrein-kinin system and fibrinolysis. We investigated the effect of heparin on the action, inhibition and secondary structure of huPK. The catalytic efficiency for the hydrolysis of substrates by huPK was determined by Michaelis-Menten kinetic plots: 5.12x10(4) M-1 s-1 for acetyl-Phe-Arg-p-nitroanilide, 1.40x10(5) M-1 s-1 for H-D-Pro-Phe-Arg-p-nitroanilide, 2.25x10(4) M-1 s-1 for Abz-Gly-Phe-Ser-Pro-Phe-Arg-Ser-Ser-Arg-Gln-EDDnp, 4.24x10(2)M-1 s-1 for factor XII and 5.58x10(2) M-1 s-1 for plasminogen. Heparin reduced the hydrolysis of synthetic substrates (by 2.0-fold), but enhanced factor XII and plasminogen hydrolysis (7.7- and 1.4-fold, respectively). The second-order rate constants for inhibition of huPK by antithrombin and C1-inhibitor were 2.40x10(2) M-1 s-1 and 1.70x10(4) M-1 s-1, respectively. Heparin improved the inhibition of huPK by these inhibitors (3.4- and 1.4-fold). Despite the fact that huPK was able to bind to a heparin-Sepharose matrix, its secondary structure was not modified by heparin, as monitored by circular dichroism. These actions may have a function in the control or maintenance of some pathophysiological processes in which huPK participates.

Genetically altered animal models in the kallikrein-kinin system

Transgenic and gene-targeting technologies allowing the generation of genetically altered animal models have greatly advanced our understanding of the function of specific genes. This is also true for the kallikrein-kinin system (KKS), in which some, but not yet all, components have been functionally characterized using such techniques. The first genetically altered animal model for a KKS component was supplied by nature, the brown Norway rat carrying an inactivating mutation in the kininogen gene. Mice deficient in tissue kallikrein, B1 and B2 receptors, some kinin-degrading enzymes, and factor XII followed, together with transgenic rat and mouse strains overexpressing tissue kallikrein, B1 and B2 receptors, and degrading enzymes. There are still no animal models with genetic alterations in plasma kallikrein, kininases I and some other degrading enzymes. The models have confirmed an important role of the KKS in cardiovascular pathology, inflammation, and pain, and have partially elucidated the distinct function of the two receptors. This created the basis for rational decisions concerning the putative use of kinin receptor agonists and antagonists in therapeutic applications. However, a more thorough analysis of the existing models and the generation of new, more sophisticated transgenic models will be necessary to clarify the still elusive issue as to where and by which mechanisms the kinins exert their actions.

Role of bradykinin B2 and B1 receptors in the local, remote, and systemic inflammatory responses that follow intestinal ischemia and reperfusion injury

The administration of bradykinin may attenuate ischemia and reperfusion (I/R) injury by acting on B(2)Rs. Blockade of B(2)R has also been shown to ameliorate lesions associated with I/R injury. In an attempt to explain these contradictory results, the objective of the present work was to investigate the role of and interaction between B(1) and B(2) receptors in a model of intestinal I/R injury in mice. The bradykinin B(2)R antagonist (HOE 140) inhibited reperfusion-induced inflammatory tissue injury and delayed lethality. After I/R, there was an increase in the expression of B(1)R mRNA that was prevented by HOE 140. In mice that were deficient in B(1)Rs (B(1)R(-/-) mice), inflammatory tissue injury was abrogated, and lethality was delayed and partially prevented. Pretreatment with HOE 140 reversed the protective anti-inflammatory and antilethality effects provided by the B(1)R(-/-) phenotype. Thus, B(2)Rs are a major driving force for B(1)R activation and consequent induction of inflammatory injury and lethality. In contrast, activation of B(2)Rs may prevent exacerbated tissue injury and lethality, an effect unmasked in B(1)R(-/-) mice and likely dependent on the vasodilatory actions of B(2)Rs. Blockade of B(1)Rs could be a more effective strategy than B(2) or B(1)/B(2) receptor blockade for the treatment of the inflammatory injuries that follow I/R.

Action of Bauhinia bauhinioides synthetic peptides on serine proteinases

The kallikrein inhibitor found in Bauhinia bauhinioides seeds (BbKI) differs from classical Kunitz plant inhibitors in the lack of disulfide bridges in its structure [Biochim. Biophys. Acta 1477 (2000) 64-74]. In this study, we examined whether structural properties may be involved in inhibitory specificity and, if so, whether those properties might be useful tools in designing compounds that interfere with enzyme activity. Peptides structurally related to the BbKI (RPGLPVRFESPLRINIIKE-NH(2)) reactive site were synthesized by solid-phase method and assayed for serine proteinase activity. The peptides RPGLPVRFESPLRINIIKE-NH(2), RPGLPVRFESPL-NH(2), and GLPVRFES-NH(2) were efficient tissue kallikrein inhibitors, with I(50) values of 0.54 microM, 0.87 microM, and 0.5mM, respectively. The lasting inhibitory effect was observed in incubation periods of up to 120 min. None of the studied peptides interfere with the activity of thrombin, factor Xa or trypsin, although the native protein BbKI is a potent trypsin inhibitor.

Angiotensin I-converting enzyme and potential substrates in human testis and testicular tumours

The angiotensin I-converting enzyme (ACE, kininase II, CD143) shows a broad specificity for various oligopeptides. Besides the well-known conversion of angiotensin I to II, ACE degrades efficiently kinins and the tetrapeptide AcSDKP (goralatide) and thus equally participates in the renin-angiotensin system, the kallikrein-kinin system, and the regulation of stem cell proliferation. In the mammalian testis, ACE occurs in two isoforms. The testicular isoform (tACE) is exclusively expressed during spermatogenesis and is generally thought to represent the germ cell-specific isozyme. However, we have previously demonstrated that, in addition to tACE, the somatic isoform (sACE) is also present in human germ cells. Similar to other oncofoetal markers, sACE exhibits a transient expression during foetal germ cell development and appears to be a constant feature of intratubular germ cell neoplasm, the so-called carcinoma-in-situ (CIS) and, in particular, of classic seminoma. This demands the existence of specific paracrine functions during male germ cell differentiation and development of male germ cell tumours, which are mediated by either of the two ACE isoforms. Considering the complexity of current data about ACE, a logical connection is required between (I) the precise localisation of ACE isoforms, (I) the local access to potential substrates and (II) functional data obtained by knockout mice models. The present article summarises the current knowledge about ACE and its potential substrates with special emphasis on the differentiation-restricted ACE expression during human spermatogenesis and prespermatogenesis, the latter being closely linked to the pathogenesis of human germ cell tumours.

Tonin and kallikrein in the brain of transgenic rat line expressing human tissue kallikrein

A transgenic rat line harboring the human tissue kallikrein gene was investigated for expression and activity of tonin and kallikrein in different regions of the brain. The introduction of the transgene into the rat genome produced a significant augmentation of the expression levels and activity of rat tissue kallikrein. The possibility that human kallikrein does not hydrolyze the rat substrate is probably responsible for the augmented expression of the rat enzyme. On the other hand, although expression of tonin was significantly reduced, tonin activity was not altered in most brain structures, except for cerebellum and neurohypophysis.

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.