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

Bradykinin B1 and B2 receptors both have protective roles in renal ischemia/reperfusion injury

To explore the role of the kallikrein-kinin system in relation to ischemia/reperfusion injury in the kidney, we generated mice lacking both the bradykinin B1 and B2 receptor genes (B1RB2R-null, Bdkrb1-/-/Bdkrb2-/-) by deleting the genomic region encoding the two receptors. In 4-month-old mice, blood pressures were not significantly different among B1RB2R-null, B2R-null (Bdkrb2-/-), and WT mice. After 30 min of bilateral renal artery occlusion and 24 h of reperfusion, mortality rates, renal histological and functional changes, 8-hydroxy-2'-deoxyguanosine levels in total DNA, mtDNA deletions, and the number of TUNEL-positive cells in the kidneys increased progressively in the following order (from lowest to highest): WT, B2R-null, and B1RB2R-null mice. Increases in mRNA levels of TGF-beta1, connective tissue growth factor, and endothelin-1 after ischemia/reperfusion injury were also exaggerated in the same order (from lowest to highest): WT, B2R-null, and B1RB2R-null. Thus, both the B1 and B2 bradykinin receptors play an important role in reducing DNA damage, apoptosis, morphological and functional kidney changes, and mortality during renal ischemia/reperfusion injury.

Kinin infusion prevents renal inflammation, apoptosis, and fibrosis via inhibition of oxidative stress and mitogen-activated protein kinase activity

The progression of renal disease displays several characteristics, including proteinuria, apoptosis, inflammation, and fibrosis. In this study, we investigated the effect of long-term infusion of kinin in protection against salt-induced renal damage in Dahl salt-sensitive rats. Dahl salt-sensitive rats were fed a high-salt diet for 2 weeks and were then infused with bradykinin (500 ng/h) via subcutaneously implanted minipumps for 3 weeks. Kinin infusion attenuated salt-induced impaired renal function as evidenced by reduced proteinuria, serum creatinine, and blood urea nitrogen levels without apparent effect on blood pressure. Morphological analysis indicated that kinin administration reduced salt-induced glomerular sclerosis, tubular dilatation, luminal protein cast formation, and interlobular arterial thickness. Kinin also significantly lowered collagen I, III, and IV deposition and their mRNA levels. Moreover, kinin reduced interstitial monocyte/macrophage accumulation, as well as tubular cell apoptosis and caspase-3 activity. Protection of renal injury by kinin was associated with increased renal NO levels and reduced nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate oxidase activities and superoxide generation. Suppression of oxidative stress by kinin was accompanied by reduced transforming growth factor-beta1 protein and mRNA levels, as well as decreased phosphorylation of mitogen-activated protein kinases. This is the first study to demonstrate that kinin infusion can directly protect against salt-induced renal injury without blood pressure reduction by inhibiting apoptosis, inflammation, and fibrosis via suppression of oxidative stress, transforming growth factor-beta1 expression, and mitogen-activated protein kinase activation.

Tissue kallikrein infusion prevents cardiomyocyte apoptosis, inflammation and ventricular remodeling after myocardial infarction

We investigated the effect of tissue kallikrein infusion on cardiac protection at acute and sub-acute phases after myocardial infarction (MI). Immediately after MI, rats were infused with purified tissue kallikrein, with or without icatibant (a kinin B2 receptor antagonist). Intramyocardial injection of kallikrein reduced myocardial infarct size and inhibited cardiomyocyte apoptosis at 1 day after MI associated with increased nitric oxide levels, Akt and glycogen synthase kinase-3beta phosphorylation and decreased caspase-3 activation. Kallikrein infusion for 7 days improved cardiac function, normalized left ventricular wall thickness and decreased monocyte/macrophage infiltration in the infarct heart. Kallikrein treatment reduced NADH oxidase expression and activity, superoxide formation and malondialdehyde levels, and reduced MAPK and Ikappa-Balpha phosphorylation, NF-kappaB activation and MCP-1 and VCAM-1 expression. Kallikrein's effects were all blocked by icatibant. These results indicate that kallikrein through kinin B2 receptor activation prevents apoptosis, inflammation and ventricular remodeling by increased nitric oxide formation and suppression of oxidative stress-mediated signaling pathways.

Influence of bradykinin B1 and B2 receptors in the immune response triggered by renal ischemia-reperfusion injury

Bradykinin B1 receptors are exclusively expressed in inflamed tissues. For this reason, they have been related with the outcomes of several pathologies. Ischemia-reperfusion injury is caused by the activation of inflammatory and cytoprotective genes, such as macrophage chemoattractant protein-1 and heme oxygenase-1, respectively. This study was aimed to analyze the involvement of bradykinin B1 and B2 receptors (B1R and B2R) in tissue response after renal ischemia-reperfusion injury. For that, B1R (B1-/-), B2R (B2-/-) knockout animals and its control (wild-type mice, B1B2+/+) were subjected to renal bilateral ischemia, followed by 24, 48 and 120 h of reperfusion. At these time points, blood serum samples were collected for creatinine and urea dosages. Kidneys were harvested for histology and molecular analyses by real-time PCR. At 24 and 48 h of reperfusion, B1-/- group resulted in the lowest serum creatinine and urea levels, indicating less renal damage, which was proved by renal histology. Renal protection associated with B1-/- mice was also related with higher expression of HO-1 and lower expression of MCP-1. In conclusion, the absence of B1R had a protective role against inflammatory responses developed after renal ischemia-reperfusion injury.

Inhibition of Angiotensin-Converting Enzyme Reduces Rat Liver Reperfusion Injury Via Bradykinin-2-Receptor

BACKGROUND

Bradykinin is both a potent vasodilatator and a central inflammatory mediator. Similar to findings in myocardial reperfusion injury, bradykinin might mediate the protective effects of angiotensin-converting enzyme (ACE) inhibition after liver ischemia via increased bradykinin-2-receptor (B-2) stimulation. On the other hand, B-2-inhibition has been shown to reduce liver reperfusion injury. This study was designed to investigate the role of Bradykinin in hepatic reperfusion injury.

MATERIALS AND METHODS

Twenty eight rats were allocated randomly to Sham procedure (Sham), 30-min normothermic ischemia (ischemia), ischemia with Ramiprilat (ACE-I), or ischemia with Ramiprilat and B-2-inhibitor HOE 140 (ACE-I+B-2-I). Liver microcirculation and leukocyte adherence were investigated using intravital microscopy 30 min after reperfusion (n = 7 per group). In addition, serum activities of AST and ALT were measured for 7 days (n = 28).

RESULTS

Ischemia was associated with a loss of perfused sinusoids, sinusoidal vasoconstriction, and a reduction in microvascular blood flow. Permanent leukocyte adherence increased both in sinusoids and in postsinusoidal venoles. ACE-I restored sinusoidal perfusion, normalized vasoregulation, maintained sinusoidal blood flow, and inhibited leukocyte adhesion. ACE-I+B-2-I abolished the protective effects linked to ACE-I. Ischemia-induced liver cell injury after 5 h of reperfusion was ameliorated by ACE-I. In the ACE-I+B-2-I group, reduction in liver cell injury was reversed.

CONCLUSION

After hepatic ischemia, ACE-I reduced reperfusion injury in a B-2-dependent manner. These results suggest a pivotal role for bradykinin in the treatment of reperfusion injury by Ramiprilat, mediating sinusoidal dilation and blunting hepatic inflammation.

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.

Selective inhibition of plasma kallikrein protects brain from reperfusion injury

We have studied the effect of DX-88, a selective recombinant inhibitor of human plasma kallikrein, in transient or permanent focal brain ischemia (with or without reperfusion, respectively) induced in C57BL/6 mice. Twenty-four hours after transient ischemia, DX-88 administered at the beginning of ischemia (pre) induced a dose-dependent reduction of ischemic volume that, at the dose of 30 microg/mouse, reached 49% of the volume of saline-treated mice. At the same dose, DX-88 was also able to reduce brain swelling to 32%. Mice treated with DX-88 pre had significantly lower general and focal deficit score. Fluoro-Jade staining, a marker for neuronal degeneration, showed that DX-88-treated mice had a reduction in the number of degenerating cells, compared with saline-treated mice. Seven days after transient ischemia, the DX-88 protective effect was still present. When the inhibitor was injected at the end of ischemia (post), it was still able to reduce ischemic volume, brain swelling, and neurological deficits. DX-88 efficacy was lost when the inhibitor was given 30 min after the beginning of reperfusion (1 h post) or when reperfusion was not present (permanent occlusion model). This study shows that DX-88 has a strong neuroprotective effect in the early phases of brain ischemia preventing reperfusion injury and indicates that inhibition of plasma kallikrein may be a useful tool in the strategy aimed at reducing the detrimental effects linked to reperfusion.

Expression and localisation of kinin receptors in colorectal polyps

Kinins increase vascular permeability as well as mitogenesis and proliferation, hence they have a potential to promote neoplasmatic transformation. In the present study we investigated the expression profile and localization of kinin B1 and B2 receptors in colorectal polyps. The biopsy samples from various polyps were obtained during endoscopy in tubular (n=18), villous (n=15) and hyperplasic polyps (n=15). The expression of genes encoding B1 and B2 was estimated by QRT-PCR TaqMan analysis. In second series B1 and B2 receptors were visualized by immunohistochemical staining in tissue specimens from colonic polyps and adjacent normal tissue. We found the highest expression of gene encoding B1 in tubular adenomas (1891 number of copies mRNA/microg total RNA+/-312 SE) which is significantly higher as compared with controls (683+/-197 SE, p<0.013). In contrast, the expression of gene for B2 was significantly increased in hyperplastic polyps (3852+/-936 SE) as compared with controls (843+/-263 SE, p<0.0016). In normal colon a well as in hyperplasic polyps B1 and B2 receptors were immunohistochemically localized in enterocytes, however in hyperplastic polyps the intensity of staining was more prominent for B2 comparing to the control group. In contrast, in tubular adenomas staining reaction for B1 was more intense than in control samples. Increased level of B1 in adenoma suggests that kinins may play a role in abnormal cellular transformation; whereas higher B2 level in hyperplasic polyp suggests its protective role. Our data may indicate that the overall effect of kinins on cellular proliferation depends on the relative level of B1 and B2 receptor expression.

Bradykinin B2receptor antagonism attenuates inflammation, mast cell infiltration and fibrosis in remote myocardium after infarction in rats

Bradykinin may interfere with myocardial remodelling by promoting inflammation and mast cell activation or, alternatively, by counteracting angiotensin II-dependent collagen accumulation. The aim of the present study was to investigate the role of bradykinin B2 receptor antagonism in inflammatory and mast cell infiltration, fibroplasia and fibrosis accumulation following myocardial infarction (MI). Myocardial infarction was produced by the ligature of the left coronary artery in male Wistar rats that were 10 weeks of age. Immediately after MI, rats received the B2 receptor antagonist Hoe140 (0.5 microg/kg per min, s.c.) or saline over a period of 3 days, 1 week or 4 weeks, constituting three separate groups and their respective controls. Coronal myocardial tissue sections underwent haematoxylin and eosin, Giemsa and picrosirius red staining, as well as immunohistochemistry for alpha-smooth muscle actin (SMA). Morphometric studies were undertaken in three different myocardial regions: MI, remote non-infarcted subendocardium (non-MI SE) and remote non-infarcted interventricular septum (non-MI IVS). The MI size was comparable between Hoe140-treated groups and their respective controls (day 3: 42 +/- 4%, n = 8, vs 43 +/- 3%, n = 6; week 1: 37 +/- 5%, n = 5, vs 39 +/- 2%, n = 5; week 4: 35 +/- 3%, n = 9, vs 36 +/- 3%, n = 7). At day 3, Hoe140 treatment reduced inflammatory cell reaction within the MI (585 +/- 59 vs 995 +/- 170 cells/mm2; P = 0.02), non-MI SE (77 +/- 12 vs 214 +/- 57 cells/mm2; P = 0.02) and non-MI IVS (93 +/- 16 vs 135 +/- 14 cells/mm2; P = 0.03) regions. Mast cells were reduced within the non-MI IVS region (0.8 +/- 0.1 vs 2.5 +/- 0.4 cells/mm2; P = 0.006), but not within the MI region. In non-MI SE, mast cells were rarely found. At week 1, Hoe140 treatment reduced alpha-SMA-positive myofibroblast infiltration within the MI (2535 +/- 383 vs 5636 +/- 968 cells/mm2; P = 0.01) and non-MI SE (222 +/- 33 vs 597 +/- 162 cells/mm2; P = 0.03) regions. In the non-MI IVS region, alpha-SMA-positive myofibroblasts were rarely found. At week 4, Hoe140 treatment reduced collagen volume fraction within the MI (37 +/- 4 vs 53 +/- 4%; P = 0.03), non-MI SE (1.3 +/- 0.2 vs 2.6 +/- 0.3%; P = 0.001) and non-MI IVS (1.1 +/- 0.2 vs 1.8 +/- 0.2%; P = 0.01) regions. Bradykinin promotes inflammation, fibroplasia and fibrosis after MI. Mast cells may have a role in fibrosis deposition through a bradykinin-related mechanism.

The tissue kallikrein-kinin system protects against cardiovascular and renal diseases and ischemic stroke independently of blood pressure reduction

Tissue kallikrein (hK1) cleaves low-molecular-weight kininogen to produce kinin peptide, which binds to kinin receptors and triggers a wide spectrum of biological effects. Tissue kallikrein levels are reduced in humans and in animal models with hypertension, cardiovascular and renal diseases. Transgenic mice or rats over-expressing human tissue kallikrein or kinin B2 receptor are permanently hypotensive, and somatic kallikrein gene delivery reduces blood pressure in several hypertensive rat models. Moreover, kallikrein gene delivery or kallikrein protein infusion can directly improve cardiac, renal and neurological function without blood pressure reduction. Kallikrein has pleiotropic effects in inhibiting apoptosis, inflammation, proliferation, hypertrophy and fibrosis, and promoting angiogenesis and neurogenesis in different experimental animal models. Kallikrein's effects can be blocked by kinin B2 receptor antagonists. Mechanistically, tissue kallikrein/kinin leads to increased nitric oxide levels and Akt activation, and reduced reactive oxygen species formation, TGF-beta1 expression, MAPK and nuclear factor-kappaB activation. Our studies indicate that tissue kallikrein, through the kinin B2 receptor and nitric oxide formation, can protect against oxidative damage in cardiovascular and renal diseases and ischemic stroke. These novel findings suggest that kallikrein/kinin may serve as new drug targets for the prevention and treatment of heart failure, renal disease and stroke in humans.

Discovery of a Dual-Function Peptide That Combines Aminopeptidase N Inhibition and Kinin B1Receptor Antagonism

Previous analyses support that aminopeptidase N is a major inactivation pathway for high-affinity peptide ligands of the human and rabbit forms of the kinin B(1) receptor (agonists or antagonists). In this study, we found that the high-affinity antagonist B-9958 (Lys-Lys-[Hyp(3), CpG(5), D-Tic(7), CpG(8)]des-Arg(9)-BK; des-Arg(9)-BK, des-arginine(9)-bradykinin) is an aminopeptidase N substrate based on its capacity to compete for the hydrolysis of the chromogenic substrate L-Ala-p-nitroanilide by membranes isolated from human or rabbit arterial smooth muscle cells, its inactivation in the presence of these membranes (radioreceptor assay) and on its intense potentiation by the aminopeptidase N inhibitor amastatin in the rabbit aorta contractility assay (gain of 0.84 units in the pA(2) scale). Analogs of B-9958 in which the N-terminal Lys residue was substituted by D-Lys or D-Arg (B-10352 and B-10356, respectively) showed reduced affinity at the human or rabbit B(1) receptors (1.2-2.8-fold), as estimated by the displacement of [(3)H]Lys-des-Arg(9)-BK binding, but were more potent antagonists of des-Arg(9)-BK-induced contraction of the rabbit aorta than B-9958 in the absence of amastatin; they were not potentiated by the latter inhibitor. Unexpectedly, B-10356 inhibited L-Ala- p-nitroanilide hydrolysis without being inactivated, suggesting that it is an aminopeptidase N inhibitor. This was verified because B-10356 (but not B-10352) potentiated peptides unrelated to kinins but susceptible to aminopeptidase N inactivation (angiotensin III, thrombin receptor hexapeptide agonist). B-10356 inhibits dual molecular targets (aminopeptidase N enzyme K(i), 0.9-2.2 microM; kinin B(1) receptor binding K(i), 0.5-1.5 nM), and this may be an advantage for specific therapeutic applications (e.g., inhibition of angiogenesis).

Mechanisms of the anti-inflammatory effects of the natural secosteroids physalins in a model of intestinal ischaemia and reperfusion injury

Reperfusion of an ischaemic tissue is associated with an intense inflammatory response and inflammation-mediated tissue injury. Physalins, a group of substances with secosteroidal chemical structure, are found in Physalis angulata stems and leaves. Here, we assessed the effects of physalins on the local, remote and systemic injuries following intestinal ischaemia and reperfusion (I/R) in mice and compared with the effects of dexamethasone. Following I/R injury, dexamethasone (10 mg kg(-1)) or physalin B or F markedly prevented neutrophil influx, the increase in vascular permeability in the intestine and the lungs. Maximal inhibition occurred at 20 mg kg(-1). Moreover, there was prevention of haemorrhage in the intestine of reperfused animals. Dexamethasone or physalins effectively suppressed the increase in tissue (intestine and lungs) and serum concentrations of TNF-alpha. Interestingly, treatment with the compounds was associated with enhancement of IL-10. The anti-inflammatory effects of dexamethasone or physalins were reversed by pretreatment with the corticoid receptor antagonist RU486 (25 mg kg(-1)). The drug compounds suppressed steady-state concentrations of corticosterone, but did not alter the reperfusion-associated increase in levels of corticosterone. The IL-10-enhancing effects of the drugs were not altered by RU486. In conclusion, the in vivo anti-inflammatory actions of physalins, natural steroidal compounds, appear to be mostly due to the activation of glucocorticoid receptors. Compounds derived from these natural secosteroids may represent novel therapeutic options for the treatment of inflammatory diseases.

NF-kappaB plays a major role during the systemic and local acute inflammatory response following intestinal reperfusion injury

1 The nuclear translocation of transcription factors may be a critical factor in the intracellular pathway involved in ischaemia/reperfusion (I/R) injury. Here, we examined whether NF-kappaB and AP-1 participated in the cascade of events leading to TNF-alpha production, neutrophil recruitment, tissue injury and lethality following intestinal I/R. 2 The superior mesenteric artery (SMA) of mice was made ischaemic for 60 min followed by 30 min of reperfusion. The effects of NF-kappaB and AP-1 were studied by the administration of the thioredoxin inhibitor, MOL-294 (methyl 4-hydroxy-4-(8-methyl-1,3-dioxo-2-phenyl-2,3,5,8-tetrahydro-1H-[1,2,4]triazolo[1,2-a]pyridazin-5-yl)but-2-ynoate), and the AP-1 inhibitor, PNRI-299 (N-benzyl-2-(3-cyanophenyl)-1,3,7-trioxo-2,3,7,8-tetrahydro-1H-[1,2,4]triazolo[1,2-a]pyridazine-5-carboxamide). After I/R, there was increase of translocation of NF-kappaB, but not of AP-1, in the intestine and lungs, as assessed by a gel shift assay. 3 Treatment with MOL-294 inhibited the increase in vascular permeability, neutrophil accumulation, hemorrhage and proinflammatory cytokine levels, induced by intestinal I/R injury in the intestine. In the lungs, MOL-294 partially inhibited edema formation, TNF-alpha production, but did not alter neutrophil recruitment. 4 Treatment with MOL-294 inhibited reperfusion-associated lethality, an effect likely to be secondary to the inhibition of systemic TNF-alpha levels. PNRI-299 had no effects on the inflammatory changes or lethality induced by I/R injury. 5 Our results point to an important role for NF-kappaB in triggering endogenous proinflammatory networks during intestinal I/R injury. Inhibition of NF-kappaB prevents tissue injury and lethality, and this was associated with inhibition of TNF-alpha production and decrease in neutrophil recruitment.

Immunolocalization and expression of kinin B1R and B2R receptors in human inflammatory bowel disease

Bradykinin is a mediator of inflammation, responsible for pain, vasodilation, and capillary permeability. Bradykinin receptor 1 (B(1)R) and bradykinin receptor 2 (B(2)R) are G protein-coupled receptors that mediate kinin effects. The latter is constitutive and rapidly desensitized; the former is induced by inflammatory cytokines and resistant to densensitization. The distribution of bradykinin receptors in human intestinal tissue was studied in patients with inflammatory bowel disease (IBD), namely ulcerative colitis (UC) and Crohn's disease (CD). Both B(2)R and B(1)R proteins are expressed in the epithelial cells of normal and IBD intestines. B(1)R protein is visualized in macrophages at the center of granulomas in CD. B(2)R protein is normally present in the apexes of enterocytes in the basal area and intracellularly in inflammatory tissue. In contrast, B(1)R protein is found in the basal area of enterocytes in normal intestine but in the apical portion of enterocytes in inflamed tissue. B(1)R protein is significantly increased in both active UC and CD intestines compared with controls. In patients with active UC, B(1)R mRNA is significantly higher than B(2)R mRNA. However, in inactive UC patients, the B(1)R and B(2)R mRNA did not differ significantly. Thus bradykinin receptors in IBD may reflect intestinal inflammation. Increased B(1)R gene and protein expression in active IBD provides a structural basis of the important role of bradykinin in chronic inflammation.

The balance between the production of tumor necrosis factor-alpha and interleukin-10 determines tissue injury and lethality during intestinal ischemia and reperfusion

A major goal in the treatment of acute ischemia of a vascular territory is to restore blood flow to normal values, i.e. to "reperfuse" the ischemic vascular bed. However, reperfusion of ischemic tissues is associated with local and systemic leukocyte activation and trafficking, endothelial barrier dysfunction in postcapillary venules, enhanced production of inflammatory mediators and great lethality. This phenomenon has been referred to as "reperfusion injury" and several studies demonstrated that injury is dependent on neutrophil recruitment. Furthermore, ischemia and reperfusion injury is associated with the coordinated activation of a series of cytokines and adhesion molecules. Among the mediators of the inflammatory cascade released, TNF-alpha appears to play an essential role for the reperfusion-associated injury. On the other hand, the release of IL-10 modulates pro-inflammatory cytokine production and reperfusion-associated tissue injury. IL-1beta, PAF and bradykinin are mediators involved in ischemia and reperfusion injury by regulating the balance between TNF-alpha and IL-10 production. Strategies that enhance IL-10 and/or prevent TNF-alpha concentration may be useful as therapeutic adjuvants in the treatment of the tissue injury that follows ischemia and reperfusion.

Endogenous Aminopeptidase N Decreases the Potency of Peptide Agonists and Antagonists of the Kinin B1Receptors in the Rabbit Aorta

The B(1) receptor for kinins is selectively stimulated by bradykinin-related fragments lacking the C-terminal arginine, des-arginine(9)-bradykinin (des-Arg(9)-BK), and Lys-des-Arg(9)-BK. The latter peptide is the optimal agonist at the human and rabbit receptor. The B(1) receptor is inducible as a function of inflammatory conditions in the vasculature. We studied the effect of endogenously expressed peptidases on the potency of ligands of this receptor in an established bioassay, the rabbit aorta contractility. The potency measured for agonists (EC(50)) or antagonists (pA(2) scale) in this assay was compared with the affinity of each agent determined using [(3)H]Lys-des-Arg(9)-BK binding competition in cultured aortic smooth muscle cells and with the competition K(i) for the hydrolysis of the aminopeptidase chromogenic substrate L-Ala-p-nitroanilide by smooth muscle cell membranes. The contractile potency of the agonist Lys-des-Arg(9)-BK is decreased by in situ metabolism, and aminopeptidase N mediates most of the distortion (inhibited by amastatin but not efficiently by puromycin). At the other end of the spectrum, the fully protected agonist Sar-[D-Phe(8)]des-Arg(9)-BK is not significantly potentiated by peptidase inhibitors. A similar distortion of apparent potency was observed for some peptide antagonists used in the contractility assay, B-10350 (Lys-Lys-[Hyp(3), Igl(5), d-Tic(7), CpG(8)]des-Arg(9)-BK) and Lys-[Leu(8)]des-Arg(9)-BK being intensely potentiated by amastatin treatment and effective L-Ala-p-nitroanilide competitors. N-Protected peptide antagonists or a nonpeptide antagonist of the B(1) receptor were not potentiated by amastatin. The coexpression of aminopeptidase N and the kinin B(1) receptor in rabbit arterial tissue is of interest for the inactivation of the high-affinity agonist Lys-des-Arg(9)-BK and for the design of hydrosoluble antagonist drugs.

International union of pharmacology. XLV. Classification of the kinin receptor family: from molecular mechanisms to pathophysiological consequences

Kinins are proinflammatory peptides that mediate numerous vascular and pain responses to tissue injury. Two pharmacologically distinct kinin receptor subtypes have been identified and characterized for these peptides, which are named B1 and B2 and belong to the rhodopsin family of G protein-coupled receptors. The B2 receptor mediates the action of bradykinin (BK) and lysyl-bradykinin (Lys-BK), the first set of bioactive kinins formed in response to injury from kininogen precursors through the actions of plasma and tissue kallikreins, whereas the B(1) receptor mediates the action of des-Arg9-BK and Lys-des-Arg9-BK, the second set of bioactive kinins formed through the actions of carboxypeptidases on BK and Lys-BK, respectively. The B2 receptor is ubiquitous and constitutively expressed, whereas the B1 receptor is expressed at a very low level in healthy tissues but induced following injury by various proinflammatory cytokines such as interleukin-1beta. Both receptors act through G alpha(q) to stimulate phospholipase C beta followed by phosphoinositide hydrolysis and intracellular free Ca2+ mobilization and through G alpha(i) to inhibit adenylate cyclase and stimulate the mitogen-activated protein kinase pathways. The use of mice lacking each receptor gene and various specific peptidic and nonpeptidic antagonists have implicated both B1 and B2 receptors as potential therapeutic targets in several pathophysiological events related to inflammation such as pain, sepsis, allergic asthma, rhinitis, and edema, as well as diabetes and cancer. This review is a comprehensive presentation of our current understanding of these receptors in terms of molecular and cell biology, physiology, pharmacology, and involvement in human disease and drug development.

Kallikrein–kinin in stroke, cardiovascular and renal disease

Tissue kallikrein, a serine proteinase, produces the potent vasodilator kinin peptide from kininogen substrate. The levels of tissue kallikrein are reduced in humans and animal models with hypertension, cardiovascular and renal disease. Using transgenic and somatic gene transfer approaches, we investigated the role of the tissue kallikrein-kinin system in cardiovascular, renal and central nervous systems. A single injection of the human tissue kallikrein gene in plasmid DNA or an adenoviral vector resulted in a prolonged reduction of blood pressure and attenuation of hypertrophy and fibrosis in the heart and kidney of several hypertensive animal models. Furthermore, enhanced kallikrein-kinin levels after gene transfer exerted beneficial effects, with protection against cardiac remodelling, renal injuries, restenosis, cerebral infarction and neurological deficits in normotensive animal models without haemodynamic effects, indicating direct actions of kallikrein independent of its ability to lower blood pressure. The effects of kallikrein were mediated by the kinin B2 receptor, as the specific B2 receptor antagonist icatibant abolished the actions of kallikrein. Moreover, kallikrein-kinin exhibited pleiotropic effects by inhibiting apoptosis, inflammation, hypertrophy and fibrosis, and promoting angiogenesis and neurogenesis in the heart, kidney, brain and blood vessel. Exogenous administration of kallikrein also led to increased nitric oxide (NO)/cGMP and cAMP levels, and reduced NAD(P)H oxidase activities, superoxide formation and pro-inflammatory cytokine levels. These results indicate a novel role of kallikrein-kinin through the kinin B2 receptor as an antioxidant and anti-inflammatory agent in protection against stroke, cardiovascular and renal disease, and may uncover new drug targets for the prevention and treatment of heart failure, vascular injury, end-stage renal disease and stroke in humans.

Restoration of depressed prostanoid-induced ileal contraction in spontaneously hypertensive rats by dietary fish oil

We have reported that dietary fish oil (FO) rich in n-3 PUFA modulates gut contractility. It was further demonstrated that the gut of spontaneously hypertensive rats (SHR) has a depressed contractility response to prostaglandins (PG) compared with normotensive Wistar-Kyoto (WKY) rats. We investigated whether feeding diets supplemented with n-3 PUFA increased gut contractility and restored the depressed prostanoid response in SHR gut. Thirteen-week-old SHR were fed diets containing fat at 5 g/100 g as coconut oil (CO), lard, canola oil containing 10% (w/w) n-3 FA as alpha-linolenic acid (1 8:3n-3), or FO (as HiDHA, 22:6n-3) for 12 wk. A control WKY group was fed 5 g/100 g CO in the diet. As confirmed, the SHR CO group had a significantly lower gut response to PGE2 and PGF2alpha compared with the WKY CO group. Feeding FO increased the maximal contraction response to acetylcholine in the ileum compared with all diets and in the colon compared with lard, and restored the depressed response to PGE2 and PGF2alpha in the ileum but not the colon of SHR. FO feeding also led to a significant increase in gut total phospholipid n-3 PUFA as DHA (22:6n-3) with lower n-6 PUFA as arachidonic acid (20:4n-6). Canola feeding led to a small increase in ileal EPA (20:5n-3) and DHA and in colonic DHA without affecting contractility. However, there was no change in ileal membrane muscarinic binding properties due to FO feeding. This report confirms that dietary FO increases muscarinic- and eicosanoid receptor-induced contractility in ileum and that the depressed prostanoid response in SHR ileum, but not colon, is restored by tissue incorporation of DHA as the active nutrient.

Clinical endocrinology and metabolism. Receptors for gut peptides

Most gut peptides exert their effects through G protein-coupled receptors, a family of about 700 membrane proteins, 87 of which are presently known to have peptide ligands. Three additional gut peptide receptors are not G protein-coupled receptors but regulate intracellular cyclic GMP accumulation. The aim of this review is to illustrate how the sequencing of the human genome and other recent advances in genomics has contributed to our understanding of the role of peptides and their receptors in gastrointestinal function. Recent discoveries include the identification of receptors for the peptides motilin and neuromedin U, and new physiological ligands for the PTH2 receptor, the CRF(2) receptor and the growth hormone secretagogue receptor. Knockout mice lacking specific peptide receptors or their ligands provide informative animal models in which to determine the functions of the numerous peptide-receptor systems in the gut and to predict which of them may be the most fruitful for drug development. Some peptide-receptor signalling systems may be more important in disease states than they are in normal physiology. For example, substance P, galanin, bradykinin and opioids play important roles in visceral pain and inflammation. Other peptides may have developmental roles: for example, disruption of endothelin-3 signalling prevents the normal development of the enteric nervous system and contributes to the pathogenesis of Hirschsprung disease.

Kinin B1 receptors: key G-protein-coupled receptors and their role in inflammatory and painful processes

Kinins are a family of peptides implicated in several pathophysiological events. Most of their effects are likely mediated by the activation of two G-protein-coupled receptors: B(1) and B(2). Whereas B(2) receptors are constitutive entities, B(1) receptors behave as key inducible molecules that may be upregulated under some special circumstances. In this context, several recent reports have investigated the importance of B(1) receptor activation in certain disease models. Furthermore, research on B(1) receptors in the last years has been mainly focused in determining the mechanisms and pathways involved in the process of induction. This was essentially favoured by the advances obtained in molecular biology studies, as well as in the design of selective and stable peptide and nonpeptide kinin B(1) receptor antagonists. Likewise, development of kinin B(1) receptor knockout mice greatly helped to extend the evidence about the relevance of B(1) receptors during pathological states. In the present review, we attempted to remark the main advances achieved in the last 5 years about the participation of kinin B(1) receptors in painful and inflammatory disorders. We have also aimed to point out some groups of chronic diseases, such as diabetes, arthritis, cancer or neuropathic pain, in which the strategic development of nonpeptidic oral-available and selective B(1) receptor antagonists could have a potential relevant therapeutic interest.

Bradykinin receptor ligands: therapeutic perspectives

Kinins, which are produced by the action of kallikrein enzymes, are blood-derived local-acting peptides that have broad effects mediated by two related G-protein-coupled receptors termed the bradykinin receptors. The endogenous kallikrein-kinin system controls blood circulation and kidney function, and promotes inflammation and pain in pathological conditions, which has led to interest in developing modulators of bradykinin receptors as potential therapeutics. This review discusses recent progress in our understanding of the genetics, molecular biology and pathophysiology of kinins and their receptors, as well as developments in medicinal chemistry, which have brought us closer to therapeutic applications of kinin receptor ligands in various indications. The potential of kinin receptor antagonists as novel analgesic agents that do not result in tolerance or have a liability for abuse has attracted particular interest.