Structural requirements for B2-agonists with improved degradation stability

Bradykinin B2 Receptor Signaling Increases Glucose Uptake and Oxidation: Evidence and Open Questions

The Kinin B2 receptor (B2R) is classically involved in vasodilation and inflammatory responses. However, through the observation of hypoglycemic effects of Angiotensin-I-Converting Enzyme (ACE) inhibitors, this protein has been related to metabolic glucose modulation in physiological and pathophysiological contexts. Although several studies have evaluated this matter, the different methodologies and models employed, combined with the distinct target organs, results in a challenge to summarize and apply the knowledge in this field. Therefore, this review aims to compile human and animal data in order to provide a big picture about what is already known regarding B2R and glucose metabolism, as well to suggest pending investigation issues aiming at evaluating the role of B2R in relation to glucose metabolism in homeostatic situations and metabolic disturbances. The data indicate that B2R signaling is involved mainly in glucose uptake in skeletal muscle and adipose tissue, acting as a synergic player beside insulin. However, most data indicate that B2R induces increased glucose oxidation, instead of storage, via activation of a broad signaling cascade involving Nitric Oxide (NO) and cyclic-GMP dependent protein kinase (PKG). Additionally, we highlight that this modulation is impaired in metabolic disturbances such as diabetes and obesity, and we provide a hypothetic mechanism to explain this blockade in light of literature data provided for this review, as well as other authors.

A review on bradykinin-related peptides isolated from amphibian skin secretion

Amphibian skin secretion has great potential for drug discovery and contributes hundreds of bioactive peptides including bradykinin-related peptides (BRPs). More than 50 BRPs have been reported in the last two decades arising from the skin secretion of amphibian species. They belong to the families Ascaphidae (1 species), Bombinatoridae (3 species), Hylidae (9 speices) and Ranidae (25 species). This paper presents the diversity of structural characteristics of BRPs with N-terminal, C-terminal extension and amino acid substitution. The further comparison of cDNA-encoded prepropeptides between the different species and families demonstrated that there are various forms of kininogen precursors to release BRPs and they constitute important evidence in amphibian evolution. The pharmacological activities of isolated BRPs exhibited unclear structure–function relationships, and therefore the scope for drug discovery and development is limited. However, their diversity shows new insights into biotechnological applications and, as a result, comprehensive and systematic studies of the physiological and pharmacological activities of BRPs from amphibian skin secretion are needed in the future.

Progress in metallocarboxypeptidases and their small molecular weight inhibitors

In what corresponds to a life span, metallocarboxypeptidases (MCPs) have jumped from being mere contaminants in animal pancreas powders (in depression year 1929) to be key players in cellular and molecular processes (in yet-another-depression years 2009-2010). MCPs are unique zinc-dependent enzymes that catalyze the breakdown of the amide bond at the C-terminus of peptide and protein substrates and participate in the recovery of dietary amino acids, tissue organogenesis, neurohormone and cytokine maturation and other important physiological processes. More than 26 genes code for MCPs in the human genome, many of them still waiting to be fully understood in terms of physiological function. A variety of MCPs have been linked to diseases in man: acute pancreatitis and pancreas cancer, type 2 diabetes, Alzheimer's Disease, various types of cancer, and fibrinolysis and inflammation. Many of these discoveries have been made possible thanks to recent advances, as exemplified by plasma carboxypeptidases N and B, known for fifty and twenty years, respectively, which have had their structures released only very recently. Plasma carboxypeptidase B is a biological target for therapy because of its involvement in the coagulation/fibrinolysis processes. Besides, the widespread use of carboxypeptidase A as a benchmark metalloprotease since the early days of Biochemistry has allowed the identification and design of an increasingly vast repertory of small molecular weight inhibitors. With these two examples we wish to emphasize that MCPs have become part of the drug discovery portfolio of pharmaceutical companies and academic research laboratories. This paper will review key developments in the discovery and design of MCP small molecular weight inhibitors, with an emphasis on the discovery of chemically diverse entities. Although encouraging advances have been achieved in the last few years, the specificity and oral bioavailability of the new chemotherapeutic agents seem to pose a challenge to medicinal chemists.

Structure-activity relationships of novel peptide agonists of the human bradykinin B2 receptor

The nonapeptide bradykinin (BK) is involved in the genesis of inflammation, edema and in pain mediation. As such, much effort has gone into the development of peptide/non-peptide antagonists to counteract these processes. However, there is an increasing awareness of the potential value of chemically stable BK agonists in the treatment of diabetes and cardiovascular diseases. In this study, a structure-activity relationship study of BK was performed to develop potent and stable peptide mimetics active at the human B2 receptors (hB2R). Twenty-three analogues were produced with substitutions at positions 1, 3, 5, 7, 8 and/or 9 of BK. In vitro binding (on transiently transfected HEK-293T cells) and biological activities (vasomotricity tests on human umbilical veins, MAPK assays on HEK-293T cells) of novel BK peptide derivatives at hB2R were determined alongside with previously reported synthetic agonists (e.g. RMP-7, JMV1609, FR190997). Some peptides were also tested in vivo in rats and rabbits using blood pressure assays. Two compounds, [Hyp(3), Thi(5), Cha(8)]-BK and [Hyp(3), Thi(5), (N)Chg(7), Thi(8)]-BK, exhibited equivalent (or even greater) in vitro affinities and potencies to BK at the naturally expressed and recombinant hB2R. Their potency and duration of action in vivo were highly superior to BK, thus inferring that they can withstand intravascular proteolysis. These novel compounds show promise as candidates for investigating the pharmacology of BK receptors and developing potential therapeutical applications.

Neutral Endopeptidase Up-Regulation in Isolated Human Umbilical Artery: Involvement in Desensitization of Bradykinin-Induced Vasoconstrictor Effects

Previous reports show that bradykinin B(2) receptors mediate contractile responses induced by bradykinin (BK) in human umbilical artery (HUA). However, although it has been reported that BK-induced responses can desensitize in several inflammatory models, the effects of prolonged in vitro incubation on BK-induced vasoconstriction in HUA have not been studied. In isolated HUA rings, BK-induced responses after a 5-h in vitro incubation showed a marked desensitization compared with responses at 2 h. Inhibition of either angiotensin-converting enzyme (ACE) or neutral endopeptidase (NEP), both BK-inactivating enzymes, failed to modify responses to BK at 2 h. After 5 h, ACE inhibition produced only a slight potentiation of BK-induced responses. In contrast, BK-induced vasoconstriction at 5 h was markedly potentiated by NEP inhibition. Moreover, NEP activity, measured by hydrolysis of its synthetic substrate (Z-Ala-Ala-Leu-p-nitroanilide), showed a 2.4-fold increase in 5-h incubated versus 2-h incubated tissues, which was completely reversed by cycloheximide (CHX) treatment. Furthermore, CHX significantly potentiated BK-induced responses, suggesting that NEP-mediated kininase activity increase at 5 h depends on de novo protein synthesis. In addition, under NEP inhibition, CHX treatment failed to produce an additional potentiation of BK-induced vasoconstriction. Still, NEP up-regulation was confirmed by Western blot, showing a 2.1-fold increase in immunoreactive NEP in 5-h incubated versus 2-h incubated HUA. In summary, the present study provides strong pharmacological evidence that NEP is up-regulated and plays a key role in desensitization of BK-induced vasoconstriction after prolonged in vitro incubation in HUA. Our results provide new insights into the possible mechanisms involved in BK-induced response desensitization during sustained inflammatory conditions.

Hypothesized and found mechanisms for potentiation of bradykinin actions

Potentiation of hormone actions can occur by different mechanisms, including inhibition of degrading enzymes, interaction with the hormone receptor leading to stabilization of bioactive conformation or leading to receptor homo- and hetero-oligomerization, receptor phosphorylation and dephosphorylation or can occur by directly influencing the signal transduction and ion channels. In this review the potentiation of bradykinin actions in different systems by certain compounds will be reviewed. Despite many long years of experimental research and investigation the mechanisms of potentiating action remain not fully understood. One of the most contradictory findings are the distinct differences between the inhibition of the angiotensin I-converting enzyme and the potentiation of the bradykinin induced smooth muscle reaction. Contradictory findings and hypothesized mechanisms in the literature are discussed in this review and in some cases compared to own results. Investigation of potentiating actions was extended from hypotension, smooth muscle reaction and cellular actions to activation of immunocompetent cells. In our opinion the potentiation of bradykinin action can occur by different mechanisms, depending on the system and the applied potentiating factor used.

Bradykinin-related peptides from Phyllomedusa hypochondrialis azurea: Mass spectrometric structural characterisation and cloning of precursor cDNAs

Amphibian skin secretions contain a plethora of bioactive compounds, many of which are understood to act to deter ingestion by predators. Bradykinins in particular are constitutively expressed in many amphibian skin secretions, mediating a variety of effects including hyperalgesia and contraction of gastric smooth muscle. Using a variety of proteomic techniques (high-performance liquid chromatography (HPLC) separation, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS), and quadrupole time-of-flight tandem mass spectrometry (Q-TOF-MS/MS)) the current study identified 13 bradykinin-like peptides in the skin secretions of Phyllomedusa hypochondrialis azurea, including several new C-terminally extended isoforms (VPPGFTPFRLT, VHypPGFTPFRQT) and a novel phyllokinin-like peptide (RPPGFTPFRVY). Identification of the cDNA sequences encoding these peptides led to the deduction that the peptides were derived from differential post-translational processing and modification of five different precursors. Such an event emphasises the metabolic efficiency of peptide production in amphibian venom, with multiple products perhaps selective to different receptors in a variety of predators generated from a single precursor. An unusual modification was also recognised in the present study, with several bradykinin-like peptides featuring hydroxyprolination of the first proline residue rather than the commonly targeted second. This alteration may be mediated by the structural organisation of N-terminal amino acids prior to precursor processing.

Potentiation of bradykinin actions by analogues of the bradykinin potentiating nonapeptide BPP9alpha

Synthetic analogues of the bradykinin potentiating nonapeptide BPP9alpha indicate significantly different structural requirements for potentiation of the bradykinin (BK)-induced smooth muscle contraction (GPI) and the inhibition of isolated somatic angiotensin I-converting enzyme (ACE). The results disprove the ACE inhibition as the only single mechanism and also the direct interaction of potentiating peptides with the bradykinin receptors in transfected COS-7 cells as molecular mechanism of potentiation. Our results indicate a stimulation of inositol phosphates (IPn) formation independently from the B2 receptor. Furthermore, the results with La3+ support the role of extracellular Ca2+ and its influx through corresponding channels. The missing effect of calyculin on the GPI disproves the role of phosphatases in the potentiating action. These experimental studies should not only contribute to a better understanding of the potentiating mechanisms but also incorporate a shift in the research towards the immune system, in particular towards the immunocompetent polymorphonuclear leukocytes. The chemotaxis of these cells can be potentiated most likely by exclusive inhibition of the enzymatic degradation of bradykinin. Thus the obtained results give evidence that the potentiation of the bradykinin action can occur by different mechanisms, depending on the system and on the applied potentiating factor.

Potentiation of kinin analogues by ramiprilat is exclusively related to their degradation

The potentiation of kinin actions represents a cardioprotective property of ACE inhibitors. Although a clear contribution to this effect is related to the inhibition of bradykinin (BK) breakdown, the high efficacy of potentiation and the ability of ACE inhibitors to provoke a B(2)-receptor-mediated response even after receptor desensitization has also triggered hypotheses concerning additional mechanisms of kinin potentiation. The application of kinin analogues with enhanced metabolic stability for the demonstration of degradation-independent mechanisms of potentiation, however, has yielded inconsistent results. Therefore, the relation between the susceptibility of B(2)-agonists to ACE and the potentiation of their actions by ACE inhibitors was investigated with the use of minimally modified kinin derivatives that varied in their degree of ACE resistance. The B(2)-agonists BK, D-Arg-[Hyp(3)]-BK, [Hyp,(3) Tyr(Me)(8)]-BK, [DeltaPhe(5)]-BK, [D-NMF(7)]-BK, and [Phe(8)psi(CH(2)-NH)Arg(9)]-BK were tested for degradation by purified rabbit ACE and for their potency in contracting the endothelium-denuded rabbit jugular vein in the absence and presence of ramiprilat. Purified ACE degraded D-Arg-[Hyp(3)]-BK and [Hyp,(3) Tyr(Me)(8)]-BK at 81% and 71% of BK degradation activity, respectively, whereas other peptides were highly ([DeltaPhe(5)]-BK) or completely ([D-NMF(7)]-BK, [Phe(8)psi(CH(2)-NH)Arg(9)]-BK) resistant. The EC(50) of BK-induced venoconstriction (1.15+/-0.2 nmol/L) was reduced by a factor of 5.7 in the presence of ramiprilat. Likewise, D-Arg-[Hyp(3)]-BK and [Hyp,(3) Tyr(Me)(8)]-BK were both significantly potentiated by a factor of 4.4, whereas the activities of the other agonists were not affected. Ramiprilat exerted no influence on the maximum contraction induced by any of the agonists. It is concluded that the potentiation of kinin analogues during ACE inhibition correlates quantitatively with the susceptibility of each substance to degradation by ACE. As such, no evidence of degradation-independent potentiating actions of ACE inhibitors could be obtained.

Linear and cyclic LFA-1 and ICAM-1 peptides inhibit T cell adhesion and function

Short peptides derived from functional proteins have been used in several instances to inhibit activity of the parent proteins. In some cases, stability and efficacy were found to be increased by cyclization of these peptides. Inhibition of interaction of the two cell adhesion counter receptors leukocyte function-associated antigen (LFA)-1 and intercellular adhesion molecule (ICAM)-1 is being studied as a method for modulating autoimmune diseases such as rheumatoid arthritis and for facilitating organ transplantation. Here, several 10-amino acid peptides derived from the contact domains of LFA-1 and ICAM-1 were evaluated for their ability to interfere with intercellular adhesion by T cells and to inhibit a more biologic, mixed lymphocyte reaction. Both linear and cyclic forms of the peptides were effective at inhibiting intercellular adhesion. Cyclic forms were effective at inhibiting T cell activation and proliferation in the mixed lymphocyte reaction.