Myelopoiesis modulation by ACE hyperfunction in kinin B1 receptor knockout mice: Relationship with AcSDKP levels

Angiotensin I-converting enzyme (ACE), a common element of renin–angiotensin system (RAS) and kallikrein–kinin system (KKS), is involved in myelopoiesis modulation, mainly by cleaving the tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP). Based on this finding and in our results showing B1 and B2 kinin receptors expression in murine bone marrow (BM) cells, we evaluated the ACE influence on myelopoiesis of kinin B1 receptor knockout mice (B1KO) using long-term bone marrow cultures (LTBMCs). Captopril and AcSDKP were used as controls. Enhanced ACE activity, expressed by non-hematopoietic cells (Ter-199^? and CD45^?), was observed in B1KO LTBMCs when compared to wild-type (WT) cells. ACE hyperfunction in B1KO cells was maintained when LTBMCs from B1KO mice were treated with captopril (1.0 μM) or AcSDKP (1.0 nM). Although no alterations were observed in ACE mRNA and protein levels under these culture conditions, 3.0 nM of AcSDKP increased ACE mRNA levels in WT LTBMCs. No alteration in the number of GM-CFC was seen in B1KO mice compared to WT animals, even when the former were treated with AcSDKP (10 μg/kg) or captopril (100 mg/kg) for 4 consecutive days. Hematological data also revealed no differences between WT and B1KO mice under basal conditions. When the animals received 4 doses of lipopolysaccharide (LPS), a decreased number of blood cells was detected in B1KO mice in relation to WT. We also found a decreased percentage of Gr1⁺/Mac-1⁺, Ter119⁺, B220⁺, CD3⁺, and Lin^?Sca1⁺c-Kit⁺ (LSK) cells in the BM of B1KO mice compared to WT animals. Low AcSDKP levels were observed in BM cultures from B1KO in comparison to WT cultures. We conclude that ACE hyperfunction in B1KO mice resulted in faster hydrolysis of AcSDKP peptide, which in turn decreased in BM tissues allowing HSC to enter the S stage of the cell cycle.     

Delayed blockade of the kinin B1 receptor reduces renal inflammation and fibrosis in obstructive nephropathy

Renal fibrosis is the common histological feature of advanced glomerular and tubulointerstitial disease leading to end-stage renal disease (ESRD). However, specific antifibrotic therapies to slow down the evolution to ESRD are still absent. Because persistent inflammation is a key event in the development of fibrosis, we hypothesized that the proinflammatory kinin B1 receptor (B1R) could be such a new target. Here we show that, in the unilateral ureteral obstruction model of renal fibrosis, the B1R is overexpressed and that delayed treatment with an orally active nonpeptide B1R antagonist blocks macrophage infiltration, leading to a reversal of the level of renal fibrosis. In vivo bone marrow transplantation studies as well as in vitro studies on renal cells show that part of this antifibrotic mechanism of B1R blockade involves a direct effect on resident renal cells by inhibiting chemokine CCL2 and CCL7 expression. These findings suggest that blocking the B1R is a promising antifibrotic therapy.     

Antitumor activity of cell-penetrant kinin B1 receptor antagonists in human triple-negative breast cancer cells

High nuclear expression of G protein-coupled receptors, including kinin B1 receptors (B1R), has been observed in several human cancers, but the clinical significance of this is unknown. We put forward the hypothesis that these “nuclearized” kinin B1R contribute to tumorigenicity and can be a new target in anticancer strategies. Our initial immunostaining and ultrastructural electron microscopy analyses demonstrated high B1R expression predominantly located at internal/nuclear compartments in the MDA-MB-231 triple-negative breast cancer (TNBC) cell line as well as in clinical samples of patients with TNBC. On the basis of these findings, in the present study, we evaluated the anticancer therapeutic potential of newly identified, cell-permeable B1R antagonists in MDA-MB-231 cells (ligand–receptor binding/activity assays and LC-MS/MS analyses). We found that these compounds (SSR240612, NG67, and N2000) were more toxic to MDA-MB-231 cells in comparison with low- or non-B1R expressing MCF-10A normal human mammary epithelial cells and COS-1 cells, respectively (clonogenic, MTT proliferative/cytocidal assays, and fluorescence-activated cell-sorting (FACS)-based apoptosis analyses). By comparison, the peptide B1R antagonist R954 unable to cross cell membrane failed to produce anticancer effects. Furthermore, the putative mechanisms underlying the anticancer activities of cell-penetrant B1R antagonists were assessed by analyzing cell cycle regulation and signaling molecules related to cell survival and apoptosis (FACS and western blot). Finally, drug combination experiments showed that cell-penetrant B1R antagonists can cooperate with suboptimal doses of chemotherapeutic agents (doxorubicin and paclitaxel) to promote TNBC death. This study provides evidence on the potential value of internally acting kinin B1R antagonists in averting growth of breast cancer.     

Evidence that kinin B2 receptor expression is upregulated by endothelial overexpression of B1 receptors

Bradykinin (BK) and des-Arg⁹-bradykinin (DBK) of kallikrein-kinin system exert its effects mediated by the B₂ (B₂R) and B₁ (B₁R) receptors, respectively. It was already shown that the deletion of kinin B₁R or of B₂R induces upregulation of the remaining receptor subtype [10], [12], [16], [28], [36]. However studies on overexpression of B₁R or B₂R in transgenic animals have supported the importance of the overexpressed receptor but the expression of another receptor subtype has not been determined [17], [19], [33]. Previous study described a marked vasodilatation and increased susceptibility to endotoxic shock which was associated with increased mortality in response to DBK in thoracic aorta from transgenic rat overexpressing the kinin B₁R (TGR(Tie₂B₁)) exclusively in the endothelium. In another study, mice overexpressing B₁R in multiple tissues were shown to present high susceptibility to inflammation and to lipopolysaccharide-induced endotoxic shock. Therefore the role of B₂R was investigated in the thoracic aorta isolated from TGR(Tie₂B₁) rats overexpressing the B₁R exclusively in the vascular endothelium. Our findings provided evidence for highly increased expression level of the B₂R in the transgenic rats. It was reported that under endotoxic shock, these rats exhibited exaggerated hypotension, bradycardia and mortality. It can be suggested that the high mortality during the pathogenesis of endotoxic shock provoked in the transgenic TGR(Tie₂B₁) rats could be due to the enhanced expression of B₂R associated with the overexpression of the B₁R.     

Renal gene expression profiling using kinin B1 and B2 receptor knockout mice reveals comparable modulation of functionally related genes

The kinin B2 receptor, which is constitutively expressed in a large number of tissues, mediates most of the known effects of bradykinin (BK). Normally undetectable in healthy tissues, the B1 receptor is strongly over-expressed under pathological conditions. BK is an important mediator in renal homeostasis and is mainly known for its natriuretic and vasodilatory effects. Recent data evidenced a role for BK in many other biological processes, such as apoptosis, development, extracellular matrix regulation and angiogenesis. In a first step to better understand how BK and its receptors could be involved in such a large variety of biological effects, we used microarray analysis to identify, under physiological conditions, the global renal gene expression profile in mice lacking either the kinin B1 or B2 receptor. Microarray experiments were performed using Agilent Mouse Oligonucleotide Microarrays (21,000 genes/microarray). Interestingly, there was a considerable number of mostly downregulated genes in both BK null mouse models compared with wild-type mice. Furthermore, a number of genes that are known to be implicated in renal physiology and/or pathology were differentially expressed in the BK null mice, which is indicative of the important role of both BK receptors in renal function.     

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.     

Cigarette smoke-induced kinin B1 receptor promotes NADPH oxidase activity in cultured human alveolar epithelial cells

Pulmonary inflammation is an important pathological feature of tobacco smoke-related lung diseases. Kinin B1 receptor (B1R) is up-regulated in the rat trachea chronically exposed to cigarette-smoke. This study aimed at determining (1) whether exposure to total particulate matter of the cigarette smoke (TPM) can induce B1R in human alveolar epithelial A549 cells, (2) the mechanism of B1R induction, (3) the functionality of de novo synthesized B1R, and (4) the role of B1R in TPM-induced increase of superoxide anion (O₂^●-) level. Results show that A549 cells exposed to 10 μg/ml TPM increased O₂^●- level along with B1R (protein and mRNA) and IL-1β mRNA. In contrast, B2R and TNF-α mRNA were not affected by TPM. The increasing effect of TPM on O₂^●- level was not significantly affected by the B1R antagonist SSR240612. TPM-increased B1R mRNA was prevented by co-treatments with N-acetyl-l-cysteine (potent antioxidant), diphenyleneiodonium (NADPH oxidase inhibitor), IL-1Ra (interleukin-1R antagonist) and SN-50 (specific inhibitor of NF-kB activation) but not by pentoxifylline (TNF-α release inhibitor), indomethacin and niflumic acid (COX-1 and -2 inhibitors). Stimulation of B1R with a selective agonist (des-Arg⁹-BK, 10 μM; 30 min) increased O₂^●-production which was prevented by apocynin and diphenyleneiodonium (NADPH oxidase inhibitors). Data suggest that the increased expression of B1R by TPM in A549 cells is mediated by oxidative stress, IL-1β and NF-kB but not by cyclooxygenases or TNF-α. The amplification of O₂^●- levels via the activation of B1R-NADPH oxidase may exacerbate pulmonary inflammation and contribute to the chronicity of tobacco smoke-related lung diseases.     

Expression of caveolin-1 enhances cholesterol efflux in hepatic cells

HepG2 cells were stably transfected with human caveolin-1 (HepG2/cav cells). Transfection resulted in expression of caveolin-1 mRNA, a high abundance of caveolin-1 protein, and the formation of caveolae on the plasma membrane. Cholesterol efflux from HepG2/cav cells was 280 and 45% higher than that from parent HepG2 cells when human plasma and human apoA-I, respectively, were used as acceptors. The difference in efflux was eliminated by treatment of cells with progesterone. There was no difference in cholesterol efflux to cyclodextrin. Cholesterol efflux from plasma membrane vesicles was similar for the two cell types. Transfection led to a 40% increase in the amount of plasma membrane cholesterol in cholesterol-rich domains (caveolae and/or rafts) and a 67% increase in the rate of cholesterol trafficking from intracellular compartments to these domains. Cholesterol biosynthesis in HepG2/cav cells was increased by 2-fold, and cholesterol esterification was reduced by 50% compared with parent HepG2 cells. The proliferation rate of transfected cells was significantly lower than that of non-transfected cells. Transfection did not affect expression of ABCA1 or the abundance of ABCA1 protein, but decreased secretion of apoA-I. We conclude that overexpression of caveolin-1 in hepatic cells stimulates cholesterol efflux by enhancing transfer of cholesterol to cholesterol-rich domains in the plasma membrane.     

Aloin enhances cisplatin antineoplastic activity in B16-F10 melanoma cells by transglutaminase-induced differentiation

Aloin, a natural anthracycline from aloe plant, is a hydroxyanthraquinone derivative shown to have antitumor properties. This study demonstrated that aloin exerted inhibition of cell proliferation, adhesion and invasion abilities of B16-F10 melanoma cells under non-cytotoxic concentrations. Furthermore, aloin induced melanoma cell differentiation through the enhancement of melanogenesis and transglutaminase activity. To improve the growth-inhibiting effect of anticancer agents, we found that the combined treatment of cells with aloin and low doses of cisplatin increases the antiproliferative activity of aloin. The results suggest that aloin possesses antineoplastic and antimetastatic properties, exerted likely through the induction of melanoma cell differentiation.     

Molecular identification and pharmacological profile of the bovine kinin B1 receptor

To support the study of kinin pharmacology in bovine models of cultured endothelial cells (ECs), the Bovine Genome Project was searched for a B1 receptor (B1R) gene ortholog (BDKRB1). A contig complementary to an intronless coding nucleotide sequence was found. The sequence was amplified from bovine EC DNA, further cloned into pcDNA3 and expressed in COS-1 cells. The bovine B1R sequence was confirmed and extended. A putative Zn2+-binding motif HEXXH is not present (replaced by HDAWP). The receptor binds [3H]Lys-des-Arg9-bradykinin in a saturable manner (K(d) 0.36 nM) and exhibits a pharmacological profile similar to that of human B(1)R.     

Doxorubicin cardiomyopathy-induced inflammation and apoptosis are attenuated by gene deletion of the kinin B1 receptor

Clinical use of the anthracycline doxorubicin (DOX) is limited by its cardiotoxic effects, which are attributed to the induction of apoptosis. To elucidate the possible role of the kinin B1 receptor (B1R) during the development of DOX cardiomyopathy, we studied B1R knockout mice (B1R(-/-)) by investigating cardiac inflammation and apoptosis after induction of DOX-induced cardiomyopathy. DOX control mice showed cardiac dysfunction measured by pressure-volume loops in vivo. This was associated with a reduced activation state of AKT, as well as an increased bax/bcl2 ratio in Western blots, indicating cardiac apoptosis. Furthermore, mRNA levels of the proinflammatory cytokine interleukin 6 were increased in the cardiac tissue. In DOX B1R(-/-) mice, cardiac dysfunction was improved compared to DOX control mice, which was associated with normalization of the bax/bcl-2 ratio and interleukin 6, as well as AKT activation state. These findings suggest that B1R is detrimental in DOX cardiomyopathy in that it mediates the inflammatory response and apoptosis. These insights might have useful implications for future studies utilizing B1R antagonists for treatment of human DOX cardiomyopathy.     

Pharmacological characterisation of novel kinin B2 receptor ligands

Peptide and nonpeptide compounds have been shown to interact specifically with B2 receptors of three different species, namely human, rabbit, and pig. Peptide agonists and nonpeptide antagonists show marked differences in potencies and suggest the existence of B2 receptor subtypes. This conclusion is based on data obtained with the modified agonist peptide LF 150943 whose potency (pEC50 9.4) is at least 100-fold higher in rabbit than in humans (7.4) and pig (6.7). The same conclusion can be drawn from data obtained with antagonists that are more potent in humans (LF 160687, pA2 9.2) than in rabbit (8.7) and pig (8.2) or with antagonists (S 1567) that show the opposite potency order, being much weaker in humans (pA2 6.9) than in rabbit (7.6) and pig (9.4). Two other compounds (FR 173657 and FR 172357) show similar pharmacological spectra as S 1567 and differ from LF 160687.     

High agonist-independent clearance of rabbit kinin B1 receptors in cultured cells

We hypothesized that the inducible kinin B(1) receptor (B(1)R) is rapidly cleared from cells when its synthesis subsides. The agonist-independent degradation of the rabbit B(1)Rs and related B(2) receptors (B(2)Rs) was investigated. Endocytosis of the B(1)R-yellow fluorescent protein (YFP) conjugate was more intense than that of B(2)R-green fluorescent protein (GFP) based on fluorescence accumulation in HEK 293 cells treated with a lysosomal inhibitor. The cells expressing B(1)R-YFP contained more GFP/YFP-sized degradation product(s) than those expressing B(2)R-GFP (immunoblot, antibodies equally reacting with both fluorescent proteins). The binding site density of B(1)R-YFP decreased in the presence of protein synthesis or maturation inhibitors (anisomycin, brefeldin A), whereas that of B(2)R-GFP remained constant. Wild-type B(1)Rs were also cleared faster than B(2)Rs in rabbit smooth muscle cells treated with metabolic inhibitors. Contractility experiments based on brefeldin A-treated isolated rabbit blood vessels also functionally support that B(1)Rs are more rapidly eliminated than B(2)Rs (decreased maximal effect of agonist over 2 h). The highly regulated B(1)R is rapidly degraded, relative to the constitutive B(2)R.     

Role of the kinin B1 receptor in insulin homeostasis and pancreatic islet function

Kinins are potent vasoactive peptides generated in blood and tissues by the kallikrein serine proteases. Two distinct kinin receptors have been described, one constitutive (subtype B2) and one inducible (subtype B1), and many physiological functions have been attributed to these receptors, including glucose homeostasis and control of vascular permeability. In this study we show that mice lacking the kinin B1 receptor (B1-/- mice) have lower fasting plasma glucose concentrations but exhibit higher glycemia after feeding when compared to wild-type mice. B1-/- mice also present pancreas abnormalities, characterized by fewer pancreatic islets and lower insulin content, which leads to hypoinsulinemia and reduced insulin release after a glucose load. Nevertheless, an insulin tolerance test indicated higher sensitivity in B1-/- mice. In line with this phenotype, pancreatic vascular permeability was shown to be reduced in B1 receptor-ablated mice. The B1 agonist desArg9bradykinin injected intravenously can induce the release of insulin into serum, and this effect was not observed in the B1-/- mice or in isolated islets. Our data demonstrate the importance of the kinin B1 receptor in the control of pancreatic vascular homeostasis and insulin release, highlighting a new role for this receptor in the pathogenesis of diabetes and related diseases.     

Effect of novel selective non-peptide kinin B(1) receptor antagonists on mouse pleurisy induced by carrageenan

Two novel selective non-peptide kinin B(1) receptor antagonists, the benzodiazepine antagonist and SSR240612, were evaluated in carrageenan-induced mouse pleurisy. The peptide R-715 (0.5 mg/kg, i.p.) and the non-peptide benzodiazepine (3 mg/kg, i.p.) antagonists significantly decreased cellular migration (predominantly neutrophils), without altering plasma exudation. SSR240612 (1 mg/kg, i.p.) diminished total cells and neutrophils, besides exudation. Oral administration of SSR240612 (10 mg/kg) also reduced total cell and neutrophil counts. Only the benzodiazepine antagonist inhibited the lung myeloperoxidase activity. No tested antagonist significantly altered the lung and pleural TNFalpha and IL-1beta production. We provide interesting evidence on the anti-inflammatory in vivo effects of non-peptide B(1) receptor antagonists.     

ApoE-dependent sterol efflux from macrophages is modulated by scavenger receptor class B type I expression

Macrophages express a number of proteins involved in sterol efflux pathways, including apolipoprotein E (apoE) and scavenger receptor class B type I (SR-BI). We have investigated a potential interaction between these two sterol efflux pathways in modulating overall macrophage sterol flux. We utilized an experimental system in which we increased expression of each of these proteins to a high physiologic range in order to perform our evaluation. We show that in apoE-expressing cells, a 4-fold increase in SR-BI expression leads to reduction of sterol and phospholipid efflux. SR-BI-mediated reduction in sterol efflux was only observed in cells that expressed endogenous apoE. In J774 cells that did not express apoE, a similar increase in SR-BI level led to increased sterol efflux. The divergent response of sterol efflux after increased SR-BI was maintained in the presence of a number of structurally diverse extracellular sterol acceptors. Increased SR-BI expression also enhanced sterol efflux to exogenously added apoE. Investigation of a potential mechanism for reduced efflux in apoE-expressing cells indicated that SR-BI expression reduced macrophage apoE by accelerating the degradation of newly synthesized apoE. This led to decreased secretion of apoE and reduced the fraction of apoE sequestered on the cell surface. Thus, enhanced SR-BI expression in macrophages can reduce the cellular level and secretion of apoE by accelerating degradation of the newly synthesized protein. This reduction of endogenous apoE is accompanied by reduced sterol efflux from macrophages.     

Prostaglandin EP4 receptor enhances BCR-induced apoptosis of immature B cells

Prostaglandin E2 (PGE2) is emerging as an important co-modulator of B cell responses. Using a pharmacological approach, we aimed to delineate the role of PGE2 in B cell receptor (BCR) induced apoptosis of immature B cells. Gene and protein expression analyses showed that, of the four PGE2 receptors subtypes, only EP4 receptor is upregulated upon BCR cross-linking, leading to sensitization of WEHI 231 cells towards PGE2 mediated inhibitory effects. EP4 receptor antagonist ONO-AE3-208, was able to completely revert the observed effects of PGE2. The engagement of EP4 receptor promotes BCR-induced G0/G1 arrest of WEHI 231 cells, resulting in enhanced caspase mediated, BCR-induced apoptosis. We addressed, mechanistically, the interplay between BCR and EP4 receptor signaling components. Prostaglandin1-alcohol (Pge1-OH), a selective EP4 receptor agonist inhibits BCR-induced activation of NF-κB by suppression of BCR-induced IκBα phosphorylation. Disruption of prosurvival pathways is a possible mechanism by which PGE2 enhances BCR-induced apoptosis in immature B lymphocytes.     

Phospholipid transfer protein interacts with and stabilizes ATP-binding cassette transporter A1 and enhances cholesterol efflux from cells

Phospholipid lipid transfer protein (PLTP) is ubiquitously expressed in animal tissues and plays multiple roles in lipoprotein metabolism, but the function of peripheral PLTP is still poorly understood. Here we show that one of its possible functions is to transport cholesterol and phospholipids from cells to lipoprotein particles by a process involving PLTP interactions with cellular ATP-binding cassette transporter A1 (ABCA1). When ABCA1 was induced in murine macrophages or ABCA1-transfected baby hamster kidney cells, PLTP gained the ability to promote cholesterol and phospholipid efflux from cells. Although PLTP alone had lipid efflux activity, its maximum activity was observed in the presence of high density lipoprotein particles. Pulsechase studies showed that the interaction of PLTP with ABCA1-expressing cells played a role in promoting lipid efflux. Overexpression of ABCA1 dramatically increased binding of both PLTP and apoA-I to common sites on the cell surface. Both PLTP and apoA-I were covalently cross-linked to ABCA1, each protein blocked cross-linking of the other, and both PLTP and apoA-I stabilized ABCA1 protein. These results are consistent with PLTP and apoA-I binding to ABCA1 at the same or closely related sites. Thus, PLTP mimics apolipoproteins in removing cellular lipids by the ABCA1 pathway, except that PLTP acts more as an intermediary in the transfer of cellular lipids to lipoprotein particles.