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Kinins exert a variety of biological actions and have been implicated in the pathogenesis of inflammation, pain, asthma, and other diseases. Kinins act through specific receptors that are widespread and belong to two major categories, B1 and B2. B2 has been cloned and shown to be of the rhodopsin type, consisting of seven hydrophobic membrane domains connected by extracellular and intracellular loops. Recent pharmacological findings from various laboratories suggest the existence of new receptor types, which have been named B3, B4, and B5. These findings are analysed critically, especially with respect to the criteria that have been used for affirming the existence of new receptor entities. The analysis is restricted to data obtained in isolated organs, almost exclusively smooth muscle preparations. Criteria for receptor characterization and classification are the order of potency of agonists and the apparent affinities of antagonists. The analysis reveals that receptors for bradykinin and related kinins are of two types, B1 and B2. B1 mediates the rapid acute response (smooth muscle contraction or relaxation) as well as some effects occurring more slowly (e.g., collagen synthesis). B1 receptor functions have been shown to be modulated by interleukins. B2 receptors are responsible for most of the kinins' biological effects, including arterial vasodilatation, plasma extravasation, venoconstriction, activation of sensory fibers (e.g., fibers for pain), and stimulation of the release of prostaglandins, endothelium-dependent relaxing factor (from endothelia), noradrenaline (from nerve terminals and adrenals), and other endogenous agents. The pharmacological characteristics of the receptor sites (B2) mediating this array of biological effects show differences between species, and two B2 receptor subtypes are proposed, namely B2A (rabbit, dog, and possibly man) and B2B (guinea pig, hamster, rat). B2A and B2B receptor subtypes have been characterized by using fairly selective agonists and competitive antagonists (e.g., D-Arg[Hyp3, D-Phe7,Leu8]BK). Noncompetitive antagonists (non-equilibrium), such as HOE 140, do not discriminate between B2A and B2B subtypes. Species differences cannot account for the multiplicity of receptors that have been proposed for rat vas deferens, pre- and post-junctional sites, and rat uterus, guinea pig ileum, and rat blood pressure. The existence of hypothetical new receptor sites was based on data obtained with partial agonists and have not been substantiated by data obtained with potent pure antagonists. The B3 receptor, proposed to explain the unusual behaviour of the guinea pig tracheal response to kinins, has to be carefully reconsidered after the finding that HOE 140 acts as a pure antagonist on this tissue and shows a fairly high affinity for the tracheal site.(ABSTRACT TRUNCATED AT 400 WORDS)

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), a natural inhibitor of pluripotent hematopoietic stem cell proliferation, has been suggested as capable of promoting an angiogenic response. We studied whether Ac-SDKP stimulates endothelial cell proliferation, migration, and tube formation; enhances angiogenic response in the rat cornea after implantation of a tumor spheroid; and increases capillary density in rat hearts with myocardial infarction (MI). In vitro, an immortal BALB/c mouse aortic endothelial 22106 cell line was used to determine the effects of Ac-SDKP on endothelial cell proliferation and migration and tube formation. In vivo, a 9L-gliosarcoma cell spheroid (250-300 microm in diameter) was implanted in the rat cornea and vehicle or Ac-SDKP (800 microg.kg(-1).day(-1) ip) infused via osmotic minipump. Myocardial capillary density was studied in rats with MI given either vehicle or Ac-SDKP. We found that Ac-SDKP 1) stimulated endothelial cell proliferation and migration and tube formation in a dose-dependent manner, 2) enhanced corneal neovascularization, and 3) increased myocardial capillary density. Endothelial cell proliferation and angiogenesis stimulated by Ac-SDKP could be beneficial in cardiovascular diseases such as hypertension and MI. Furthermore, because Ac-SDKP is mainly cleaved by ACE, it may partially mediate the cardioprotective effect of ACE inhibitors.

The anti-inflammatory peptide Ac-SDKP is released from thymosin-␤4 by renal meprin-␣ and prolyl oligopeptidase. Am J Physiol Renal Physiol 310: F1026 -F1034, 2016. First published March 9, 2016 doi:10.1152/ajprenal.00562.2015.-N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a natural tetrapeptide with antiinflammatory and antifibrotic properties. Previously, we have shown that prolyl oligopeptidase (POP) is involved in the Ac-SDKP release from thymosin-␤4 (T␤4). However, POP can only hydrolyze peptides shorter than 30 amino acids, and T␤4 is 43 amino acids long. This indicates that before POP hydrolysis takes place, T␤4 is hydrolyzed by another peptidase that releases NH2-terminal intermediate peptide(s) with fewer than 30 amino acids. Our peptidase database search pointed out meprin-␣ metalloprotease as a potential candidate. Therefore, we hypothesized that, prior to POP hydrolysis, T␤4 is hydrolyzed by meprin-␣. In vitro, we found that the incubation of T␤4 with both meprin-␣ and POP released Ac-SDKP, whereas no Ac-SDKP was released when T␤4 was incubated with either meprin-␣ or POP alone. Incubation of T␤4 with rat kidney homogenates significantly released Ac-SDKP, which was blocked by the meprin-␣ inhibitor actinonin. In addition, kidneys from meprin-␣ knockout (KO) mice showed significantly lower basal Ac-SDKP amount, compared with wild-type mice. Kidney homogenates from meprin-␣ KO mice failed to release Ac-SDKP from T␤4. In vivo, we observed that rats treated with the ACE inhibitor captopril increased plasma concentrations of Ac-SDKP, which was inhibited by the coadministration of actinonin (vehicle, 3.1 Ϯ 0.2 nmol/l; captopril, 15.1 Ϯ 0.7 nmol/l; captopril ϩ actinonin, 6.1 Ϯ 0.3 nmol/l; P Ͻ 0.005). Similar results were obtained with urinary Ac-SDKP after actinonin treatment. We conclude that release of Ac-SDKP from T␤4 is mediated by successive hydrolysis involving meprin-␣ and POP.N-acetyl-seryl-aspartyl-lysyl-proline; thymosin-␤4; meprin-␣; prolyl oligopeptidase; angiotensin-converting enzyme THE ANTI-INFLAMMATORY PEPTIDE N-acetyl-seryl-aspartyl-lysylproline (Ac-SDKP) was identified originally in the bone marrow (24). It has also been widely distributed in mammalian organs, plasma, urine, and circulating mononuclear cells (23,39,46). In animal diseases with hypertension, as well as cardiovascular and kidney disease, Ac-SDKP reduces inflammatory cell infiltration and collagen deposition in the heart, kidney, lung, and liver (14,15,33,34,37,44). Ac-SDKP is hydrolyzed by angiotensin-converting enzyme (ACE) and has a short half-life of 4.5 min in the circulation (16). Treatment with ACE inhibitors significantly increased plasma concentration of Ac-SDKP (2), and some of the ACE inhibitors protective effects were reported to be mediated by the increases in Ac-SDKP concentrations (34, 35).Thymosin-␤4 (T␤4) is a major G-actin-sequestering peptide that consists of 43 amino acids. Since it contains the Ac-SDKP sequence in its NH 2 -terminal, T␤4 is considered to be the precursor of 39). Our group has shown p...

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