Differential induction of functional B1-bradykinin receptors along the rat nephron in endotoxin induced inflammation

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.

Early kidney damage induced by subchronic exposure to PM2.5 in rats

BACKGROUND

Particulate matter exposure is associated with respiratory and cardiovascular system dysfunction. Recently, we demonstrated that fine particles, also named PM_2.5, modify the expression of some components of the angiotensin and bradykinin systems, which are involved in lung, cardiac and renal regulation. The endocrine kidney function is associated with the regulation of angiotensin and bradykinin, and it can suffer damage even as a consequence of minor alterations of these systems. We hypothesized that exposure to PM_2.5 can contribute to early kidney damage as a consequence of an angiotensin/bradykinin system imbalance, oxidative stress and/or inflammation.

RESULTS

After acute and subchronic exposure to PM_2.5, lung damage was confirmed by increased bronchoalveolar lavage fluid (BALF) differential cell counts and a decrease of surfactant protein-A levels. We observed a statistically significant increment in median blood pressure, urine volume and water consumption after PM_2.5 exposure. Moreover, increases in the levels of early kidney damage markers were observed after subchronic PM_2.5 exposure: the most sensitive markers, β-2-microglobulin and cystatin-C, increased during the first, second, sixth and eighth weeks of exposure. In addition, a reduction in the levels of specific cytokines (IL-1β, IL-6, TNF-α, IL-4, IL-10, INF-γ, IL-17a, MIP-2 and RANTES), and up-regulated angiotensin and bradykinin system markers and indicators of a depleted antioxidant response, were also observed. All of these effects are in concurrence with the presence of renal histological lesions and an early pro-fibrotic state.

CONCLUSION

Subchronic exposure to PM_2.5 induced an early kidney damage response that involved the angiotensin/bradykinin systems as well as antioxidant and immune imbalance. Our study demonstrates that PM_2.5 can induce a systemic imbalance that not only affects the cardiovascular system, but also affects the kidney, which may also overall contribute to PM-related diseases.

Bradykinin receptor blockade restores the baroreflex control of renal sympathetic nerve activity in cisplatin-induced renal failure rats

AIM

This study investigated the effect of renal bradykinin B1 and B2 receptor blockade on the high- and low-pressure baroreceptor reflex regulation of renal sympathetic nerve activity (RSNA) in rats with cisplatin-induced renal failure.

METHODS

Cisplatin (5 mg/kg) or saline was given intraperitoneally 4 days prior to study. Following chloralose/urethane anaesthesia, rats were prepared for measurement of mean arterial pressure (MAP), heart rate and RSNA and received intrarenal infusions of either Lys-[des-Arg⁹ , Leu⁸ ]-bradykinin (LBK), a bradykinin B1 receptor blocker, or bradyzide (BZ), a bradykinin B2 receptor blocker. RSNA baroreflex gain curves and renal sympatho-inhibitory responses to volume expansion (VE) were obtained.

RESULTS

In the control and renal failure groups, basal MAP (89 ± 3 vs. 80 ± 8 mmHg) and RSNA (2.0 ± 0.3 vs. 1.7 ± 0.6 μV.s) were similar but HR was lower in the latter group (331 ± 8 vs. 396 ± 9 beats/min). The baroreflex gain for RSNA in the renal failure rats was 39% (P < 0.05) lower than the control but was restored to normal values following intrarenal infusion of BZ, but not LBK. VE had no effect on MAP or HR but reduced RSNA by some 40% (P < 0.05) in control but not renal failure rats. Intrarenal LBK infusion in the renal failure rats normalized the VE induced renal sympatho-inhibition whereas BZ only partially restored the response.

CONCLUSION

These findings suggest that pro-inflammatory bradykinin acting at different receptors within the kidney generates afferent neural signals which impact differentially within the central nervous system on high- and low-pressure regulation of RSNA.

Activation of mTORC1 in collecting ducts causes hyperkalemia

Mutation of TSC (encoding tuberous sclerosis complex protein) and activation of mammalian target of rapamycin (mTOR) have been implicated in the pathogenesis of several renal diseases, such as diabetic nephropathy and polycystic kidney disease. However, the role of mTOR in renal potassium excretion and hyperkalemia is not known. We showed that mice with collecting-duct (CD)-specific ablation of TSC1 (CDTsc1KO) had greater mTOR complex 1 (mTORC1) activation in the CD and demonstrated features of pseudohypoaldosteronism, including hyperkalemia, hyperaldosteronism, and metabolic acidosis. mTORC1 activation caused endoplasmic reticulum stress, columnar cell lesions, and dedifferentiation of CD cells with loss of aquaporin-2 and epithelial-mesenchymal transition-like phenotypes. Of note, mTORC1 activation also reduced the expression of serum- and glucocorticoid-inducible kinase 1, a crucial regulator of potassium homeostasis in the kidney, and decreased the expression and/or activity of epithelial sodium channel-α, renal outer medullary potassium channel, and Na(+), K(+)-ATPase in the CD, which probably contributed to the aldosterone resistance and hyperkalemia in these mice. Rapamycin restored these phenotypic changes. Overall, this study identifies a novel function of mTORC1 in regulating potassium homeostasis and demonstrates that loss of TSC1 and activation of mTORC1 results in dedifferentiation and dysfunction of the CD and causes hyperkalemia. The CDTsc1KO mice provide a novel model for hyperkalemia induced exclusively by dysfunction of the CD.

Bradykinin receptor 1 activation exacerbates experimental focal and segmental glomerulosclerosis

Focal and segmental glomerulosclerosis (FSGS) is one of the most important causes of end-stage renal failure. The bradykinin B1 receptor has been associated with tissue inflammation and renal fibrosis. To test for a role of the bradykinin B1 receptor in podocyte injury, we pharmacologically modulated its activity at different time points in an adriamycin-induced mouse model of FSGS. Estimated albuminuria and urinary protein to creatinine ratios correlated with podocytopathy. Adriamycin injection led to loss of body weight, proteinuria, and upregulation of B1 receptor mRNA. Early treatment with a B1 antagonist reduced albuminuria and glomerulosclerosis, and inhibited the adriamycin-induced downregulation of podocin, nephrin, and α-actinin-4 expression. Moreover, delayed treatment with antagonist also induced podocyte protection. Conversely, a B1 agonist aggravated renal dysfunction and even further suppressed the levels of podocyte-related molecules. Thus, we propose that kinin has a crucial role in the pathogenesis of FSGS operating through bradykinin B1 receptor signaling.

Strong cytotoxic effect of the bradykinin antagonist BKM-570 in ovarian cancer cells--analysis of the molecular mechanisms of its antiproliferative action

The standard chemotherapy for epithelial ovarian cancer (EOC) patients is currently a combination of taxane and platinum. However, most EOC patients still suffer relapses, and there is an immediate need for the development of novel and more effective therapeutic modalities against this deadly disease. Recently, the nonpeptide bradykinin (BK) antagonist 2,3,4,5,6-pentafluorocinnamoyl-(o-2,6-dichlorobenzyl)-l-tyrosine-N-(4-amino-2,2,6,6-tetramethyl-piperidyl) amide (BKM-570) was shown to cause impressive growth inhibition of lung and prostate tumors, displaying superior in vivo inhibitory effects than convential chemotherapeutic drugs. Here, we investigated BKM-570 cytotoxic effects in two EOC cell lines, derived from different EOC histopathologies: a clear cell carcinoma (TOV-21), and an endometrioid carcinoma (TOV-112). We showed that BKM-570 effectively inhibited the growth of ovarian cancer cells, as its cytotoxic effects were comparable to those of cisplatin, and were independent of the functional status of BK receptors. Moreover, BKM-570 synergized with cisplatin in inhibiting EOC cell growth. To better understand the molecular mechanisms of the antiproliferative action of this BK antagonist in EOC cells, we performed gene expression profiling in TOV-21 and TOV-112 cells following treatment with 10 μM BKM-570 for 24 h. BKM-570 displayed similar cytotoxic effects in the two cell lines analyzed, as genes with previously shown involvement in apoptosis/antiapoptosis and cell adhesion were proportionally upregulated and downregulated in both cell lines, whereas genes involved in basic cellular mechanisms, including cell growth and maintenance, metabolism, cell cycle control, inflammatory and immune response, signal transduction, protein biosynthesis, transcription regulation, and transport, were predominantly downregulated upon treatment. Our data are indicative of the therapeutic potential of BKM-570 and related compounds in EOC management.

Blockade of the kinin B1 receptor ameloriates glomerulonephritis

Severe inflammation characterizes rapidly progressive glomerulonephritides, and expression of the kinin B1 receptor (B1R) associates with inflammation. Delayed B1R blockade reduces renal inflammation in a model of unilateral ureteral obstruction, but whether B1R modulates the pathophysiology of glomerulonephritides is unknown. Here, we observed an association of B1R protein expression and inflammation, in both glomeruli and the renal interstitium, in biopsies of patients with glomerulonephritides, Henoch-Schönlein purpura nephropathy, and ANCA-associated vasculitis. In the nephrotoxic serum-induced glomerulonephritis model, we observed upregulation of the B1R receptor; treatment with a B1R antagonist beginning 2 weeks after the onset of disease reduced both glomerular and tubular lesions and improved renal function. B1R blockade reduced renal chemokine expression and macrophage accumulation. Collectively, our data demonstrate that blockade of the kinin B1R has significant potential for the treatment of glomerulonephritis.

Ontogeny of bradykinin B1 receptors in the mouse kidney

Kinins are vasoactive peptides that stimulate two G-protein coupled bradykinin receptors (B1R and B2R). B2R-knockout mice are salt sensitive and develop renal dysgenesis and hypertension if salt stressed during embryogenesis. B1R-knockout mice, on the other hand, are protected from inflammation and fibrosis. This study examined the spatiotemporal expression of B1R during renal organogenesis. The segmental nephron identity of B1R immunoreactivity was determined by costaining with markers of the collecting duct (Dolichos biflorus), proximal tubule (Dolichos tetraglonus), and nephron progenitors (Pax2). At E14.5, the B1R was confined to few cells in the metanephric mesenchyme. Abundance of B1R increased progressively during development. On E17.5, B1R was enriched in differentiating proximal tubular cells and by postnatal day 1, B1R was clearly expressed on the luminal aspect of the proximal tubule. Quantitative real-time PCR revealed that the levels of B1R mRNA more than double during renal maturation. We conclude that 1) B1R expression correlates closely with nephron maturation; 2) lack of B1R in nephron progenitors suggests that B1R is unlikely to play a role in early nephrogenesis; and 3) enrichment of B1R in maturing proximal tubule suggests a potential role for this receptor in terminal differentiation of the proximal nephron.

Angiotensin II-induced hypertension regulates AT1 receptor subtypes and extracellular matrix turnover in mouse retinal pigment epithelium

Accumulation of specific deposits and extracellular molecules under the retinal pigment epithelium (RPE) has been previously observed in eyes with age-related macular degeneration (AMD) and may play a role in the pathogenesis of AMD. Even though age is the major determinant for developing AMD, clinical studies have revealed hypertension (HTN) as another systemic risk factor. Angiotensin II (Ang II) is considered the most important hormone associated with HTN. To evaluate the relationship of Ang II to AMD, we studied whether mouse RPE expresses functional Ang II receptor subtypes and whether HTN-induced Ang II regulates expression of these receptors as well as critical ECM molecules (MMP-2 and type IV collagen) involved in ECM turnover in RPE. We used 9-month-old C57BL/6 male mice infused with Ang II alone or Ang II in combination with the AT1 receptor antagonist candesartan or the AT2 receptor antagonist PD123319 for 4 weeks to determine whether HTN-associated Ang II was important for ECM regulation in RPE. We found that mouse RPE expressed both Ang II receptor subtypes at the mRNA and protein levels. Infusion with Ang II induced HTN and elevated plasma and ocular Ang II levels. Ang II also regulated AT1a and AT1b receptor mRNA expression, the intracellular concentration of calcium [Ca(2+)](i), MMP-2 activity, and type IV collagen accumulation. Concurrent administration of Ang II with the AT1 receptor blocker prevented the increase in blood pressure and rise in ocular Ang II levels, as well as the calcium and MMP-2 responses. In contrast, the type IV collagen response to Ang II was prevented by blockade of AT2 receptors, but not AT1 receptors. Plasma Ang II levels were not modified by the AT1 or AT2 receptor blockade. Since the effects of Ang II on MMP-2 and type IV collagen require inhibition of both Ang II receptor subtypes, these receptors may play a role as a potential therapeutic targets to prevent ECM turnover dysregulation in the RPE basement membrane, suggesting a pathogenic mechanism to explain the link between HTN and AMD.

The kallikrein-kinin system in health and in diseases of the kidney

Since kallikrein was discovered as a vasodilatory substance in human urine, the kallikrein-kinin system (KKS) has been considered to play a physiological role in controlling blood pressure. Gene targeting experiments in mice in which the KKS has been inactivated to varying degrees have, however, questioned this role, because basal blood pressures are not altered. Rather, these experiments have shown that the KKS has a different and important role in preventing changes associated with normal senescence in mice, and in reducing the nephropathy and accelerated senescence-associated phenotypes induced in mice by diabetes. Other experiments have shown that the KKS suppresses mitochondrial respiration, partly by nitric oxide and prostaglandins, and that this suppression may be a key to understanding how the KKS influences senescence-related diseases. Here we review the logical progression and experimental data leading to these conclusions, and discuss their relevance to human conditions.

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.

Hemodynamic and renal involvement of B1 and B2 kinin receptors during the acute phase of endotoxin shock in mice

B1 kinin receptor (B1R) is up-regulated by endotoxins and thus may represent a therapeutic target in sepsis. We investigated the expression and role of B1R and B2R in the acute phase of lipopolysaccharide (LPS)-induced endotoxin shock in C57BL/6 mice (WT) and B1R and B2R knock out mice (B1KO, B2KO). B1R mRNA was enhanced from 6 to 48 h after LPS while B2R mRNA was further increased in B1KO. Maximal hypotension was found 24 h after LPS, and was more pronounced in B1KO, but was reduced in B2KO. Glomerular filtration rate was more reduced by LPS in B1KO than in WT and B2KO. Glycemia was reduced by LPS and particularly in B1KO and B2KO mice. Mortality was increased by LPS in B1KO. These data suggest that the up-regulated B1R plays, at least transiently, a significant beneficial role in acute LPS-induced hypotension. Conversely, supra activation of B2R could be also involved in the increased mortality observed in B1KO mice.

High glucose increases B1-kinin receptor expression and signaling in endothelial cells

The loss of endothelial function is the initiating factor in the development of diabetic vascular disease. Kinins control endothelial function by the activation of two receptors: the B2 which is constitutively expressed, and the B1 which is highly induced in pathological conditions. In the present study, we observed that the levels of B1-receptor mRNA and protein are induced in endothelial cells incubated in high glucose. An increase in B1-receptor was also observed in the endothelial layer of aortas, from 4-week diabetic rats. When cells were grown in high glucose, the B1 agonist des-Arg9-BK increased nitrite levels, whereas in normal glucose nitrite levels were unchanged. Nitrite increase was blocked by L-NAME and 1400W indicating the participation of the inducible Nitric Oxide Synthase (iNOS). iNOS protein levels were also increased in high glucose. These results demonstrate the participation of the B1 receptor in the signaling pathways mediated by kinins in high glucose.

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.

Mechanism of bradykinin-induced Ca2+ mobilization in murine proximal tubule epithelial cells

Despite the recognized physiological role of bradykinin (BK) in the kidney in maintaining glomerular and tubule function and its role in pathological states such as endotoxemia, diabetes, and other diseases, relatively little is known about the mechanisms by which BK can impact kidney function. Furthermore, the signaling of BK receptors in the murine nephron has not been fully characterized. The present studies were undertaken to examine BK-stimulated Ca(2+) signaling using Fura-2 in the murine proximal tubule epithelial cell line TKPTS. BK produced a concentration-dependent rise in intracellular Ca(2+) ([Ca(2+)])(i) (pEC(50) = 8.39 +/- 0.04). Selective antagonists showed the rise in [Ca(2+)](i) was mediated through B2 receptors. The rise in [Ca(2+)](i) was rapid and reversible and was maximally stimulated at 1 microM (697 +/- 70 nM above basal level of 115 +/- 6 nM). Studies with thapsigargin and EGTA showed Ca(2+) mobilization was dependent on two events: release and influx. Both U73122 (1-[6-[[17-beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione) [a phospholipase C (PLC) inhibitor] and genistein (a tyrosine kinase inhibitor) partially inhibited BK-stimulated rise in [Ca(2+)](i). When combined, both agents produced a further decrease, suggesting multiple pathways for PLC activation may be involved. The ability of Ni(2+) to inhibit influx indicated the activation of a Ca(2+) release-activated channel (CRAC). Ca(2+) mobilization did not seem to be affected by cyclic nucleotides or protein kinase C. In summary, the TKPTS murine proximal tubule cell line expresses functional B2 receptors linked to Ca(2+) mobilization that is dependent on phospholipase C and activation of CRAC.

Renal protective role of bradykinin B1 receptor in stroke-prone spontaneously hypertensive rats

The kallikrein-kinin system plays important roles in blood pressure regulation, metabolism of electrolytes and organ protection. Although the bradykinin B2 receptor (B2R) has been reported to be involved in most of these effects, a role of the bradykinin B1 receptor (B1R) has also been noted recently. The aim of this study was to determine the role of renal B1R in stroke-prone spontaneously hypertensive rats (SHR-SP). Sixteen-week-old SHR-SP and Wistar Kyoto rats (WKY) as a control were used in the experiments. A high level of B1R mRNA was detected in SHR-SP, while the expression in WKY was almost undetectable. Immunohistochemistry revealed a B1R protein in the renal tubules and glomeruli in SHR-SP. The acute injection of a B1 R agonist into SHR-SP increased urinary NOx excretion to a level up to 5-fold higher than that in the SHR-SP treated with vehicle. The infusion of B1 R antagonist for 4 weeks resulted in a significant elevation of blood pressure and urinary albumin excretion and a decrease in urinary NOx excretion in SHR-SP. The administration of B1 R antagonist resulted in renal interstitial and glomerular fibrosis in SHR-SP. Moreover, the expressions of transforming growth factor (TGF) beta1 protein and collagen III mRNA in SHR-SP treated with B1R antagonist were significantly higher than those of SHR-SP treated with a vehicle. The expression and phosphorylation of extracellular signal-regulated protein kinase (ERK) and p38, but not c-Jun N-terminal kinase (JNK), were significantly increased in the SHR-SP treated with B1R antagonist. These results indicated that renal B1R might be over-expressed in a high blood pressure condition, and that this upregulated B1 R may play an important role in renal protection by inhibiting renal fibrosis via an increase of NO production and a suppression of TGFbeta1 expression and mitogen-activated protein kinase (ERK and p38) phosphorylation.

Kinin B1 receptor up-regulation after lipopolysaccharide administration: role of proinflammatory cytokines and neutrophil influx

Several studies have now clearly established the ability of LPS to induce bradykinin B(1) receptor up-regulation in vivo and the functional relevance of this up-regulation for the pathophysiological effects of LPS. Using an in vivo system in which LPS is injected locally into the rat paw, we have examined the potential contribution of proinflammatory cytokines, NF-kappaB activation, and neutrophil influx for the functional and molecular up-regulation of the bradykinin B(1) receptor. Treatment with LPS resulted in a rapid and sustained functional up-regulation of B(1) receptors in the rat paw that correlated with the increase in B(1) receptor mRNA levels. B(1) receptor up-regulation is preceded by the rapid activation of the transcription factor NF-kappaB and the production of proinflammatory cytokines, including TNF-alpha and IL-1beta. More importantly, blockade of NF-kappaB translocation, TNF-alpha, or IL-1beta prevented the functional and molecular up-regulation of B(1) receptors. Injection of LPS also induced the influx of neutrophils that followed the peak of cytokine production and associated with the persistent activation of NF-kappaB and functional B(1) receptor up-regulation. Blockade of neutrophil influx with platelet-activating factor receptor antagonists or cell adhesion molecule blockers prevented B(1) receptor up-regulation. Thus, by acting in cooperation and in a coordinated, timely manner, TNF-alpha, IL-1beta, neutrophils, and the transcription factor NF-kappaB are major and essential players in the ability of LPS to induce B(1) receptor expression in vivo.

Bradykinin induces a calcium-store- dependent calcium influx in mouse mesangial cells

Bradykinin (BK) elicits extracellular-dependent [Ca2+](i) elevations in mouse mesangial cells (MMC) that are not blocked by verapamil, nifedipine, L-nicardipine, NiCl(2), or LaCl(3). The aim of the present study was to evaluate the mechanisms involved in calcium influx induced by BK in MMC. [Ca2+](i) was analyzed through spectrofluorometry employing fura-2-AM, and the data were expressed as [Ca2+](i )obtained/[Ca2+](i )basal ratio. Heparin (IP(3), a receptor antagonist) almost abolished the effects of BK in MMC (1.85 +/- 0.15 vs. 1.13 +/- 0.02, n = 4, p = 0.001). Following external and intracellular calcium store depletion, BK's effect was absent even after successful extracellular calcium replenishment. ML-7 (a myosin light chain kinase inhibitor) blocked responses to thapsigargin (2.62 +/- 0.13 vs. 1.11 +/- 0.04, n = 4, p < 0.001), but not those of BK (6.51 +/- 0.39, n = 6, vs. 5.86 +/- 1.17, n = 4, p = 0.39). On the other hand, genistein (a tyrosine kinase inhibitor) was able to inhibit thapsigargin (3.12 +/- 0.22, n = 5, vs. 1.28 +/- 0.16, n = 4, p < 0.001) as well as BK responses (6.46 +/- 0.66 vs. 2.89 +/- 0.61, n = 4, p < 0.05). Econazole (a P-450 monooxygenase inhibitor) inhibited the responses to both thapsigargin (3.45 +/- 0.16 vs. 1.03 +/- 0.03, n = 4, p < 0.001) and BK (6.49 +/- 0.83, n = 6, vs. 1.17 +/- 0.08, n = 4, p = 0.01). Finally, responses to BK were not affected by indomethacin (6.69 +/- 0.66 vs. 6.57 +/- 0.87, n = 4, p = 0.916). Thus, BK promotes an IP(3)-sensitive store-dependent calcium influx in MMC. This phenomenon seems to involve tyrosine kinase and P-450 monooxygenase products in its transduction pathway.

Kallikrein cascade and cytokines in inflamed joints

Rheumatoid arthritis is a chronic multi-system disease of unknown aetiology. The current hypothesis is that an unknown antigen triggers an autoimmune response in a genetically susceptible individual. The predominant pathological change is that of an inflammatory synovitis, characterised by cellular infiltrates and angiogenesis, with subsequent bone and cartilage destruction. These pathological changes are as a result of the activation of a variety of cells, inflammatory mediators, and effector molecules. The pro-inflammatory kinins and cytokines appear to play a central role in the pathogenesis of rheumatoid arthritis. Sufficient evidence exists that establishes a key role for the kallikrein-kinin cascade in inflamed joints. In addition, there appears to be an inter-relationship between cytokines and kinins in the inflammatory process. Kinins induce the release of cytokines, and cytokines have been shown to augment the effects of kinins. This may lead to an enhancement and perpetuation of the inflammatory process. In this review, we report a first study, correlating markers of disease with the kallikrein-kinin cascade and with cytokines.

Induction of functional bradykinin b(1)-receptors in normotensive rats and mice under chronic Angiotensin-converting enzyme inhibitor treatment

BACKGROUND

The physiological effects of ACE inhibitors may act in part through a kinin-dependent mechanism. We investigated the effect of chronic ACE-inhibitor treatment on functional kinin B(1)- and B(2)-receptor expression, which are the molecular entities responsible for the biological effects of kinins.

METHODS AND RESULTS

Rats were subjected to different 6-week treatments using various mixtures of the following agents: ACE inhibitor, angiotensin AT(1)-receptor antagonist, and B(1)- and B(2)-receptor antagonists. Chronic ACE inhibition induced both renal and vascular B(1)-receptor expression, whereas B(2)-receptor expression was not modified. Furthermore, with B(1)-receptor antagonists, it was shown that B(1)-receptor induction was involved in the hypotensive effect of ACE inhibition. Using microdissection, we prepared 10 different nephron segments and found ACE-inhibitor-induced expression of functional B(1)-receptors in all segments. ACE-inhibitor-induced B(1)-receptor induction involved homologous upregulation, because it was prevented by B(1)-receptor antagonist treatment. Finally, using B(2)-receptor knockout mice, we showed that ACE-inhibitor-induced B(1)-receptor expression was B(2)-receptor independent.

CONCLUSIONS

This study provides the first evidence that chronic ACE-inhibitor administration is associated with functional vascular and renal B(1)-receptor induction, which is involved in ACE-inhibitor-induced hypotension. The observed B(1)-receptor induction in the kidney might participate in the known renoprotective effects of ACE inhibition.

Different sensitivity to nephrotoxic agents and osmotic stress in proximal tubular and collecting duct cell lines derived from transgenic mice

We established six renal tubular cell lines from definite tubular areas of the kidney of transgenic mice harboring tsSV40 large T-antigen gene. Three are proximal tubular cell lines prepared from the S(1), S(2) and S(3) segments of the proximal tubule and the others are collecting duct cell lines obtained from cortical, outer medullary and inner medullary collecting ducts (CCD, OMCD and IMCD, respectively). To verify the growth properties of these cell lines under different temperature conditions (33 and 39 degrees C), two representative cells were chosen from the proximal tubule (S(1) cells) and from the collecting duct (IMCD cells). From these cells, a daily change in cell number was evaluated as a parameter of cell growth. As might be expected, cell numbers of these cells increased only at 33 degrees C. Similar patterns were also observed with the other cell lines. To observe the different sensitivity to nephrotoxic agents in proximal tubular cell lines, the cells were exposed to nephrotoxic agent, gentamicin, ochratoxin A or cisplatin. Gentamicin (1 mg/ml) dose-dependently decreased cellular ATP levels of the S(1) cells only. In contrast, the effect of ochratoxin A (10(-6) M) was most pronounced in the S(2) cells, and that of cisplatin (10 microg/ml) in the S(3) cells. To characterize collecting duct cell lines, a hyperosmotic challenge of 700 or 1100 mOsm/l was applied to the cells. At an isoosmotic condition of 300 mOsm/l, the number of cells from the collecting ducts, regardless of their origin, increased continuously during the culture period of 4 days. At an osmotic concentration of 700 mOsm/l, the number of CCD cells decreased, while OMCD cells showed a gradual but a significant increase in cell numbers throughout the culture period. IMCD cells, however, proliferated even at a concentration as high as 1100 mOsm/l, although an initial decrease in cell number was noted on the first day of culture. For confirmation of intracellular free calcium ([Ca(2+)](i)) mobilization, cells were treated with ATP and bradykinin. The [Ca(2+)](i) was increased significantly and immediately by ATP (10(-4) M) in S(1) cells and bradykinin (10(-7) M) in IMCD cells. From the results obtained, it is indicated that renal tubular cell lines from transgenic mice have different sensitivities to nephrotoxic or osmotic stress showing the conservation of the functional characters of the definite part it originated from.

Endotoxin sensitization to kinin B(1) receptor agonist in a non-human primate model: haemodynamic and pro-inflammatory effects

1. Although endotoxaemia induces kinin B(1) receptors in several animal models, this condition is not documented in primates. This study examined the up-regulation of haemodynamic and pro-inflammatory responses to the B(1) agonist des-Arg(10)-kallidin (dKD) in a non-human primate model. 2. Green monkeys (Cercopithecus aethiops St Kitts) received lipopolysaccharide (LPS; 90 microg kg(-1)) or saline intravenously. After 4 h, anaesthetized monkeys were cannulated via the carotid artery to monitor blood pressure changes following intra-arterial injections of dKD or the B(2) agonist bradykinin (BK). Oedema induced by subcutaneous kinin administration was evaluated as the increase in ventral skin folds in anaesthetized monkeys injected with captopril at 4 h to 56 days post-LPS. 3. LPS increased rectal temperature but did not affect blood pressure after 4 h. dKD reduced blood pressure (E(max): 27+/-4 mmHg; EC(50): 130 pmol kg(-1)) and increased heart rate (E(max): 33 b.p.m.) only after LPS. In contrast, the dose-dependent fall in blood pressure with BK was comparable in all groups. The selective B(1) antagonist [Leu(9)]dKD (75 ng kg(-1) min(-1), intravenously) abolished responses to dKD but not BK. 4. dKD injection induced oedema dose-dependently (2.4+/-0.1 mm at 150 nmol) only following LPS (at 4 h to 12 days but not 56 days). In contrast, BK-induced oedema was present and stable in all monkeys. Co-administration of [Leu(9)]dKD (150 nmol) significantly reduced oedema induced by dKD (50 nmol). 5. These results suggest LPS up-regulation of B(1) receptor effects in green monkeys. This non-human primate model may be suitable for testing new, selective B(1) antagonists with therapeutic potential as anti-inflammatory agents.

Lipopolysaccharide enhances bradykinin-induced signal transduction via activation of Ras/Raf/MEK/MAPK in canine tracheal smooth muscle cells

Bacterial lipopolysaccharide (LPS) was found to induce inflammatory responses and to enhance bronchial hyperreactivity to several contractile agonists. However, the implication of LPS in the pathogenesis of bronchial hyperreactivity was not completely understood. Therefore, in this study, we investigated the effect of LPS on mitogen-activated protein kinase (MAPK) activation associated with potentiation of bradykinin (BK)-induced inositol phosphates (IPs) accumulation and Ca(2+) mobilization in canine cultured tracheal smooth muscle cells (TSMCs). LPS stimulated phosphorylation of p42/p44 MAPK in a time- and concentration-dependent manner using a Western blot analysis against a specific phosphorylated form of MAPK antibody. Maximal stimulation of the p42 and p44 MAPK isoforms occurred after 7 min-incubation and the maximal effect was achieved with 100 microg ml(-1) LPS. Pretreatment of TSMCs with LPS potentiated BK-induced IPs accumulation and Ca(2+) mobilization. However, there was no effect on the IPs response induced by endothelin-1, 5-hydroxytryptamine, and carbachol. In addition, pretreatment with PDGF-BB enhanced BK-induced IPs response. These enhancements by LPS and PDGF-BB might be due to an increase in BK B(2) receptor density (B(max)) in TSMCs, characterized by competitive inhibition of [(3)H]-BK binding using B(1) and B(2) receptor-selective reagents. The enhancing effects of LPS and PDGF-BB were attenuated by PD98059, an inhibitor of MAPK kinase (MEK), suggesting that the effect of LPS may share a common signalling pathway with PDGF-BB in TSMCs. Furthermore, overexpression of dominant negative mutants, H-Ras-15A and Raf-N4, significantly suppressed p42/p44 MAPK activation induced by LPS and PDGF-BB, indicating that Ras and Raf may be required for activation of these kinases. These results suggest that the augmentation of BK-induced responses produced by LPS might be, at least in part, mediated through activation of Ras/Raf/MEK/MAPK pathway in TSMCs.

Bradykinin B(1) receptor-mediated changes in renal hemodynamics during endotoxin-induced inflammation

Kinins have been shown to influence renal hemodynamics and function. Under physiologic conditions, most kinin effects involve bradykinin B(2) receptors, but bradykinin B(1) receptors are often induced during inflammation. The purpose of this study was to examine in vivo the effects of bradykinin B(1) receptor activation on renal hemodynamics under normal and inflammatory conditions. In anesthetized rats, activation of bradykinin B(1) receptors by arterial infusion of bradykinin B(1) receptor agonist des-Arg(9)-bradykinin reduced renal plasma flow and GFR. Prior administration (18 h) of lipopolysaccharide to induce inflammation resulted in a larger bradykinin B(1) receptor-induced reduction in renal plasma flow. Values of other parameters remained unchanged, thus resulting in an increased filtration fraction. The presence and the functionality of the bradykinin B(1) receptor at the level of glomerular afferent and efferent arterioles were studied by mRNA expression analysis and intracellular calcium ([Ca(2+)](i)) mobilization studies. Stimulation with des-Arg(9)-bradykinin of microdissected afferent arterioles from control and lipopolysaccharide-treated rats induced [Ca(2+)](i) mobilization without any significant difference in amplitude between control and lipopolysaccharidetreated rats. However, des-Arg(9)-bradykinin only induced [Ca(2+)](i) mobilization in efferent arterioles from lipopolysaccharide-treated rats. It is suggested that activation of bradykinin B(1) receptors located along the efferent arteriole may participate in the modification of renal hemodynamics in inflammatory states.

Vascular kinin B(1) and B(2) receptor-mediated effects in the rat isolated perfused kidney - differential regulations

1. Bradydykinin (BK) and analogs acting preferentially at kinin B(1) or B(2) receptors were tested on the rat isolated perfused kidney. Kidneys were perfused in an open circuit with Tyrode's solution. Kidneys preconstricted with prostaglandin F(2alpha) were used for the analysis of vasodilator responses. 2. BK induced a concentration-dependent renal relaxation (pD(2)=8.9+/-0.4); this vasodilator response was reproduced by a selective B(2) receptor agonist, Tyr(Me)(8)-BK (pD(2)=9.0+/-0.1) with a higher maximum effect (E(max)=78.9+/-6.6 and 55.8+/-4.3% of ACh-induced relaxation respectively, n=6 and 19, P<0.02). Icatibant (10 nM), a selective B(2) receptor antagonist, abolished BK-elicited relaxation. Tachyphylaxis of kinin B(2) receptors appeared when repeatedly stimulated at 10 min intervals. 3. Des-Arg(9)-BK, a selective B(1) receptor agonist, induced concentration-dependent vasoconstriction at micromolar concentration. Maximum response was enhanced in the presence of lisinopril (1 microM) and inhibited by R 715 (8 microM), a selective B(1) receptor antagonist. Des-Arg(9)-[Leu(8)]-BK behaved as an agonist. 4. A contractile response to des-Arg(9)-BK occurred after 1 of perfusion and increased with time by a factor of about three over a 3 h perfusion. This post-isolation sensitization to des-Arg(9)-BK was abolished by dexamethasone (DEX, 30 mg kg(-1) i.p., 3 h before the start of the experiment and 10 microM in perfusate) and actinomycin D (2 microM). Acute exposure to DEX (10 microM) had no effect on sensitized des-Arg(9)-BK response, in contrast to indomethacin (30 microM) that abolished it. DEX pretreatment however had no effect on BK-induced renal vasodilation. 5. Present results indicate that the main renal vascular response to BK consists of relaxation linked to the activation of kinin B(2) receptors which rapidly desensitize. Renal B(1) receptors are also present and are time-dependently sensitized during the in vitro perfusion of the rat kidneys.