Evidence for activation of the tissue kallikrein-kinin system in nociceptive transmission and inflammatory responses of mice using a specific enzyme inhibitor

Enkephalin related peptides are released from jejunum wall by orally ingested bromelain

Stem bromelain [EC 3.4.22.32] is a thiol-endopeptidase and orally recommended in traditional medicine due to its analgesic activity, but the mechanisms are not known. Proenkephalin is expressed in the nervous system, but also in the gastrointestinal tract, where it can be assessed by ingested stem bromelain. Here we demonstrated that stem bromelain hydrolyses synthetic proenkephalin fragments after basic amino acid residues flanking the enkephalin sequences. We also observed with in vivo studies that oral administration of bromelain reduced jejunum proenkephalin levels and increased the serum enkephalin in mice. Effective anti-nociceptive effects in mice were observed 3 h after oral administration of 3 mg/kg stem bromelain by the acetic acid-induced writhing test. However, with higher doses this effect is reduced due to hydrolysis of enkephalin that possibly occurs by the presence of ananain in commercial pineapple stem bromelain preparations, that is also a thiol-protease with broad specificity. The analgesic effects were also evaluated by hot-plate and formalin tests and the obtained results indicated that enkephalin generated in intestine acts in periphery where it also can have anti-inflammatory activity.

Mouse mast cells and mast cell proteases do not play a significant role in acute tissue injury pain induced by formalin

Subcutaneous formalin injections are used as a model for tissue injury-induced pain where formalin induces pain and inflammation indirectly by crosslinking proteins and directly through activation of the transient receptor potential A1 receptor on primary afferents. Activation of primary afferents leads to both central and peripheral release of neurotransmitters. Mast cells are found in close proximity to peripheral sensory nerve endings and express receptors for neurotransmitters released by the primary afferents, contributing to the neuro/immune interface. Mast cell proteases are found in large quantities within mast cell granules and are released continuously in small amounts and upon mast cell activation. They have a wide repertoire of proposed substrates, including Substance P and calcitonin gene-related peptide, but knowledge of their in vivo function is limited. We evaluated the role of mouse mast cell proteases (mMCPs) in tissue injury pain responses induced by formalin, using transgenic mice lacking either mMCP4, mMCP6, or carboxypeptidase A3 (CPA3), or mast cells in their entirety. Further, we investigated the role of mast cells in heat hypersensitivity following a nerve growth factor injection. No statistical difference was observed between the respective mast cell protease knockout lines and wild-type controls in the formalin test. Mast cell deficiency did not have an effect on formalin-induced nociceptive responses nor nerve growth factor-induced heat hypersensitivity. Our data thus show that mMCP4, mMCP6, and CPA3 as well as mast cells as a whole, do not play a significant role in the pain responses associated with acute tissue injury and inflammation in the formalin test. Our data also indicate that mast cells are not essential to heat hypersensitivity induced by nerve growth factor.

Flavonoid-metal ion complexes: a novel class of therapeutic agents

Flavonoids are among the most investigated phytochemicals due to their pharmacological and therapeutic activities. Their ability to chelate with metal ions has resulted in the emergence of a new category of molecules with a broader spectrum of pharmacological activities. However, the biological significance of these flavonoid-metal ion complexes is yet to be completely explored. Moreover, no concerted efforts have been made to elucidate their molecular targets and mechanisms of action. This review attempts to provide a snapshot of the various biological activities reported for flavonoid-metal ion complexes and their potential as therapeutic agents. Understanding the mechanism of action and the influence of structure will provide a strong basis to design novel flavonoid-metal ion complexes of therapeutic significance.

Cyclic, linear, cycloretro-isomer, and cycloretro-inverso peptides derived from the C-terminal sequence of bradykinin as substrates or inhibitors of serine and cysteine proteases

We investigated the inhibition of trypsin, human tissue (hK1) and human plasma kallikrein (HuPK), papain, and cathepsin L, B, and X by synthetic cyclic, cycloretro-isomer, cycloretro-inverso, and linear peptides derived from the C-terminal sequence of bradykinin. c(FSPFRG) and Ac-FSPFRG-NH2 were taken as the references for cyclic and linear peptides, respectively. Longer and more flexible analogs of them with addition of 2, 3, or 4 Gly and cycloretro-isomer and cycloretro-inverso analogs of c(FSPFRG) and c(GGGFSPFRG) were obtained and assayed. The susceptibility to hydrolysis of the peptides to all proteases was also examined. The highest affinities were found for c(FSPFRG) with hK1, Ac-GGFSPFRG-NH2 with HuPK, and psi (NHCO) c(fspfrG) with cathepsin L. The Ki values for cathepsin B and X with cyclic peptides were lower than those of linear peptides. The serine proteases hydrolyzed all linear and cyclic peptides, except c(FSPFRG) and c(GFSPFRG). The cysteine proteases hydrolyzed only the linear peptides, which were poor substrates. Although the Ki values obtained in the current work were in the microM range, the cyclic and cycloretro-inverso peptides seem to be a promising approach to develop efficient and resistant to hydrolysis inhibitors for the kallikreins and lysosomal cysteine proteases.

Kininogenase activity of Thalassophryne nattereri fish venom

Accidents caused by the venomous fish Thalassophryne nattereri are characterized by edema, intense pain and necrosis at the site of the sting. This study assessed the nociceptive and edematogenic activities of T. nattereri venom after injection into the mouse hindpaw and determination of the paw licking duration and weight. Subplantar injections of the venom (0.1-6 microg) induced a dose-related increase of the paw licking time and paw swelling with maximal values at 3 microg (209.5 +/- 57.5 s and 135.0 +/- 6.8 mg, respectively). Pretreatment of mice with either indomethacin (10 mg/kg, i.p.), a cyclooxygenase inhibitor, dexamethasone (1 mg/kg, s.c.), a steroid anti-inflammatory agent, cyproheptadine (1 mg/kg, i.p.), antagonist of serotonin receptors or L-NAME (100 mg/kg, s.c.), inhibitor of nitric oxide syntase, did not affect the venom-induced nociceptive and edematogenic responses. Injection of the opioid analgesic fentanyl (0.1 mg/kg, s.c.) reduced the paw licking time induced by 1 microg venom by 84% of control, without affecting the paw swelling. Both nociceptive and edematogenic responses were reduced after treatment with a specific tissue kallikrein inhibitor (TKI, 100 mg/kg, i.p.) by 78% and 24% from control values, respectively. Administration of a specific plasma kallikrein inhibitor (PKSI(527,) 100 mg/kg, s.c.) did not affect the venom-induced nociceptive response, but it decreased the paw edema by 15% from control. After injection of the angiotensin-converting enzyme inhibitor captopril (100 mg/kg, i.p.) the venom-induced nociceptive end edematogenic responses were increased by two-fold. The role of kallikreins possibly present in the venom was further assessed by hydrolysis of human kininogen and kininogen-derived synthetic peptides, showing the release of kallidin (Lys-bradykinin). The hydrolysis was inhibited by metal chelating agents but not by serino-, aspartyl- or cysteino-proteinase inhibitors. The data suggest that a protease with tissue-kallikrein-like activity plays a major role in nociception and edema induced by T. nattereri venom and this should be considered to achieve efficient treatments for human accidents with this venom.

Differences in substrate and inhibitor sequence specificity of human, mouse and rat tissue kallikreins

The kininogenase activities of mouse (mK1), rat (rK1) and human (hK1) tissue kallikreins were assayed with the bradykinin-containing synthetic peptides Abz-MTEMARRPPGFSPFRSVTVQNH2 (where Abz stands for o-aminobenzoyl) and Abz-MTSVIRRPPGFSPFRAPRV-NH2, which correspond to fragments Met374-Gln393 and Met375-Val393 of mouse and rat LMWKs (low-molecular-mass kininogens) with the addition of Abz. Bradykinin was released from these peptides by the mK1- and rK1-mediated hydrolysis of Arg-Arg and Arg-Ser (or Arg-Ala) peptide bonds. However, owing to preferential hydrolysis of Phe-Arg compared with the Arg-Ala bond in the peptide derived from rat LMWK, hK1 released bradykinin only from the mouse LMWK fragment and preferentially released des-[Arg9]bradykinin from the rat LMWK fragment (Abz-MTSVIRRPPGFSPFRAPRV-NH2). The formation of these hydrolysis products was examined in more detail by determining the kinetic parameters for the hydrolysis of synthetic, internally quenched fluorescent peptides containing six N- or C-terminal amino acids of bradykinin added to the five downstream or upstream residues of mouse and rat kininogens respectively. One of these peptides, Abz-GFSPFRAPRVQ-EDDnp (where EDDnp stands for ethylenediamine 2,4-dinitrophenyl), was preferentially hydrolysed at the Phe-Arg bond, confirming the potential des-[Arg9]bradykinin-releasing activity of hK1 on rat kininogen. The proline residue that is two residues upstream of bradykinin in rat kininogen is, in part, responsible for this pattern of hydrolysis, since the peptide Abz-GFSPFRASRVQ-EDDnp was preferentially cleaved at the Arg-Ala bond by hK1. Since this peptidase accepts the arginine or phenylalanine residue at its S1 subsite, this preference seems to be determined by the prime site of the substrates. These findings also suggested that the effects observed in rats overexpressing hK1 should consider the activation of B1 receptors by des-[Arg9]bradykinin. For further comparison, two short internally quenched fluorescent peptides that bind to hK1 with affinity in the nM range and some inhibitors described previously for hK1 were also assayed with mK1 and rK1.

Characterisation of local inflammatory response induced by Thalassophryne nattereri fish venom in a mouse model of tissue injury

The Thalassophryne nattereri fish venom induces a severe burning pain, oedema, and necrosis observed both clinically and experimentally. The present study was carried out in order to describe the pattern of local acute inflammatory response after T. nattereri venom injection. Our findings show that the edematogenic response induced by T. nattereri venom in footpad of mice was dose- and time dependent, and remained significantly elevated over 48 h after injection. Analysis of footpad homogenates were tested for the presence of TNF-alpha, IL-1beta and IL-6, and demonstrated augmented levels of these cytokines. Our results showed that the injection of venom developed an inadequate cellular inflammatory response evidenced by poor infiltration of mononuclear cells, preceded by decreased number of these cells in peripheral blood. In contrast, we observed an early intense recruitment of neutrophil to peritoneal cavity, accompanied by a significant decrease in the number of mononuclear cells. A drastic increase in the total amount of cells, mainly in neutrophils, followed by mononuclear cell recruitment was observed 24 h. In addition, we also demonstrated that T. nattereri venom affects the viability of mononuclear cells (J774A1) in culture. We conclude that the scarcity of inflammatory cellular influx into local lesions (intraplantar) induced by T. nattereri venom could be a consequence of an impaired blood flow in venules at injured tissue and cytotoxic effect of the venom on inflammatory cells can contribute to this impairment.

Role of the bradykinin B2 receptor for the local and systemic inflammatory response that follows severe reperfusion injury

1. Bradykinin (BK) appears to play an important role in the development and maintenance of inflammation. Here, we assessed the role of the BK B(2) receptor for the injuries that occur after ischemia and reperfusion (I/R) of the territory irrigated by the superior mesenteric artery. 2. Tissue (lung and duodenum) kallikrein activity increased after ischemia with greater enhancement after reperfusion. A selective inhibitor of tissue kallikrein, Phenylacetyl-Phe-Ser-Arg-N-(2,3-dinitrophenyl)-ethylenediamine (TKI, 0.001-10 mg ml(-1)), inhibited kallikrein activity in a concentration-dependent manner in vitro. In vivo, pretreatment with TKI (30 mg kg(-1)) prevented the extravasation of plasma and the recruitment of neutrophils. 3. Similarly, the bradykinin B(2) receptor antagonists, HOE 140 (0.01-1.0 mg kg(-1)) or FR173657 (10.0 mg kg(-1)), inhibited reperfusion-induced increases in vascular permeability and the recruitment of neutrophils in the intestine and lungs. 4. In a model of more severe I/R injury, HOE 140 (1.0 mg kg(-1)) inhibited the increase in vascular permeability, neutrophil recruitment, haemorrhage and tissue pathology. Furthermore, HOE 140 significantly inhibited the elevations of TNF-alpha in tissue and serum and partially prevented lethality. This was associated with an increase in the concentrations of IL-10 in tissue and serum. 5. Thus, our results demonstrate that, following intestinal I/R injury, there is an increase in tissue kallikrein activity and activation of BK B(2) receptors. B(2) receptor activation is essential for the development of inflammatory tissue injury and lethality. These results contrast with those of others showing that BK mostly exerts a protective role during I/R injury.

Role of kinins and sensory neurons in the rat pleural leukocyte migration induced by Phoneutria nigriventer spider venom

The leukocyte migration induced by Phoneutria nigriventer spider venom (PNV) has been investigated in rats using the pleurisy model. Intrapleural injection of PNV (10-100 microg/cavity) caused a dose- and time-dependent leukocyte accumulation. The bradykinin B(2) receptor antagonist Hoe 140 (0.5 mg/kg) substantially inhibited PNV-induced cell accumulation, whereas the angiotensin-converting enzyme inhibitor captopril (2 mg/kg) potentiated by 80% this effect. The non-specific kallikrein inhibitor aprotinin and the plasma kallikrein inhibitor soybean trypsin inhibitor greatly reduced PNV-induced leukocyte migration, whereas the selective tissue kallikrein inhibitor P(ac)-F-S-R-EDDnp failed to affect PNV-induced responses. Treatment of rats with capsaicin (50 mg/kg) at the neonatal stage resulted in 67% inhibition of the PNV-induced cell migration. The neurokinin NK(1) receptor antagonist SR140333, but not the NK(2) receptor antagonist SR48968, reduced by 55% venom-induced cell accumulation. We conclude that bradykinin generation is involved in the PNV-induced pleural leukocyte migration in rats, where it can directly activate sensory nerves contributing to a neurogenic inflammatory mechanism.

Inflammatory pain: kinins and antagonists

This short review focuses on the most recent findings in the rapidly expanding field of kinin research. Through a series of recent publications, the crucial relevance of this group of peptides as mediators of inflammatory pain is becoming increasingly evident. On the strength of this idea, kinins have been implicated as algogen peptides produced in response to noxious stimuli. The importance of kinins has been elucidated by different pharmacological and molecular approaches. Special attention has been given to studies with selective kinin antagonists, as well as to the use of receptor gene deletion technology. The gathering of results has demonstrated that both B(1) and B(2) receptors seem to exert a meaningful role during nociceptive responses, the B(1) receptor being most relevant in the chronic stages of inflammatory pain. It is hoped that new effective and useful therapeutic agents, mainly B(1) kinin selective receptor antagonists, might soon be available.