Kinins and kinin receptors in the nervous system

Kinin-mediated inflammation in neurodegenerative disorders

The mediatory role of kinins in both acute and chronic inflammation within nervous tissues has been widely described. Bradykinin, the major representative of these bioactive peptides, is one of a few mediators of inflammation that directly stimulates afferent nerves due to the broad expression of specific kinin receptors in cell types in these tissues. Moreover, kinins may be delivered to a site of injury not only after their production at the endothelium surface but also following their local production through the enzymatic degradation of kininogens at the surface of nerve cells. A strong correlation between inflammatory processes and neurodegeneration has been established. The activation of nerve cells, particularly microglia, in response to injury, trauma or infection initiates a number of reactions in the neuronal neighborhood that can lead to cell death after the prolonged action of inflammatory substances. In recent years, there has been a growing interest in the effects of kinins on neuronal destruction. In these studies, the overexpression of proteins involved in kinin generation or of kinin receptors has been observed in several neurologic disorders including neurodegenerative diseases such Alzheimer's disease and multiple sclerosis as well as disorders associated with a deficiency in cell communication such as epilepsy. This review is focused on recent findings that provide reliable evidence of the mediatory role of kinins in the inflammatory responses associated with different neurological disorders. A deeper understanding of the role of kinins in neurodegenerative diseases is likely to promote the future development of new therapeutic strategies for the control of these disorders. An example of this could be the prospective use of kinin receptor antagonists.

Kinin generation from exogenous kininogens at the surface of retinoic acid-differentiated human neuroblastoma IMR-32 cells after stimulation with interferon-γ

Bradykinin-related peptides, kinins, ubiquitously occur in the nervous system and together with other pro-inflammatory mediators contribute to pathological states of that tissue such as edema and chronic pain. In the current work we characterized the kinin-forming system of neuronal cells obtained by differentiation of human neuroblastoma cell line IMR-32 with retinoic acid. These cells were shown to concentrate exogenous kinin precursors, kininogens, on the surface, release kinins from kininogens and subsequently convert kinins to their des-Arg metabolites. Significantly higher amounts of kinins and des-Arg-kinins were produced after cell stimulation with interferon-γ, a potent pro-inflammatory mediator involved in many neurological disorders. The expression of the major tissue kininogenase (the human kallikrein 1) and the major cell membrane-bound kininase (the carboxypeptidase M) also increased after cell stimulation with interferon-γ, suggesting the involvement of these enzymes in the kinin production and degradation, respectively. Interferon-γ was also able to up-regulate the expression of two known subtypes of kinin receptors. On the protein level, the changes were only observed in the expression of the des-Arg-kinin-specific type 1 receptor which functions in the propagation of the inflammatory state. Taken together, these results suggest a novel way for local kinin and des-Arg-kinin generation in the nervous tissue during pathological states accompanied by interferon-γ release.

Differential regulation of inducible and endothelial nitric oxide synthase by kinin B1 and B2 receptors

Kinins are vasoactive peptides that play important roles in cardiovascular homeostasis, pain and inflammation. After release from their precursor kininogens, kinins or their C-terminal des-Arg metabolites activate two distinct G protein-coupled receptors (GPCR), called B2 (B2R) or B1 (B1R). The B2R is expressed constitutively with a wide tissue distribution. In contrast, the B1R is not expressed under normal conditions but is upregulated by tissue insult or inflammatory mediators. The B2R is considered to mediate many of the acute effects of kinins while the B1R is more responsible for chronic responses in inflammation. Both receptors can couple to Galphai and Galphaq families of G proteins to release mediators such as nitric oxide (NO), arachidonic acid, prostaglandins, leukotrienes and endothelium-derived hyperpolarizing factor and can induce the release of other inflammatory agents. The focus of this review is on the different transduction events that take place upon B2R and B1R activation in human endothelial cells that leads to generation of NO via activation of different NOS isoforms. Importantly, B2R-mediated eNOS activation leads to a transient ( approximately 5min) output of NO in control endothelial cells whereas in cytokine-treated endothelial cells, B1R activation leads to very high and prolonged ( approximately 90min) NO production that is mediated by a novel signal transduction pathway leading to post-translational activation of iNOS.

The use of kinin B1 and B2 receptor knockout mice and selective antagonists to characterize the nociceptive responses caused by kinins at the spinal level

The mechanisms by which kinins induce hyperalgesia in the spinal cord were investigated by using B(1) or B(2) knockout mice in conjunction with kinin selective agonists and antagonists. The i.t. administration of the kinin B(2) receptor agonists, bradykinin (BK) or Tyr(8)-BK produced dose-related thermal hyperalgesia evaluated in the hot-plate test. BK-induced hyperalgesia was abolished by the B(2) receptor antagonist Hoe 140. The i.t. injection of the kinin B(1) receptor agonists, des-Arg(9)-bradykinin (DABK) or des-Arg(10)-kallidin (DAKD) also caused dose-related thermal hyperalgesia. Different from the B(2) agonists, the i.t. injection of DABK or DAKD caused a weak, but prolonged hyperalgesia, an effect that was blocked by the B(1) receptor antagonist des-Arg(9)-[Leu(8)]-bradykinin (DALBK). The i.t. injection of BK caused thermal hyperalgesia in wild-type mice (WT) and in the B(1) receptor knockout mice (B(1)R KO), but not in the B(2) receptor knockout mice (B(2)R KO). Similarly, the i.t. injection of DABK elicited thermal hyperalgesia in WT mice, but not in B(1)R KO mice. However, DABK-induced hyperalgesia was more pronounced in the B(2)R KO mice when compared with the WT mice. The i.t. injection of Hoe 140 or DALBK inhibited the second phase of formalin (F)-induced nociception. Furthermore, i.t. Hoe 140, but not DALBK, also inhibits the first phase of F response. Finally, the i.t. injection of DALBK, but not of Hoe 140, inhibits the long-term thermal hyperalgesia observed in the ipsilateral and in contralateral paws after intraplantar injection with complete Freund's adjuvant. These findings provide evidence that kinins acting at both B(1) and B(2) receptors at the spinal level exert a critical role in controlling the nociceptive processing mechanisms. Therefore, selective kinin antagonists against both receptors are of potential interest drugs to treat some pain states.

Bradykinin levels in dental pulp by microdialysis

Bradykinin is a potent mediator of pain and inflammation. To examine extracellular levels of bradykinin in human dental pulp, CMA/20 microdialysis probes were inserted into the pulp tissue of 22 teeth diagnosed with normal pulp or with irreversible pulpitis before their extraction or endodontic therapy. Probes were perfused with a modified Locke-Ringer's buffer and bradykinin levels in the dialysate evaluated using a radioimmunoassay. Mean extracellular levels of bradykinin within pulp tissue diagnosed with irreversible pulpitis were significantly higher (262.26 +/- 83.79 fmol/ml) than that found within normal pulp (19.41 +/- 6.47 fmol/ml). Highest levels of bradykinin were detected in pulp tissue diagnosed with irreversible pulpitis when the patient had reported pain in the past, compared with patients who were in pain just before their visit. These observations suggest that the bradykinin system is activated during pulpitis and may contribute to pain and inflammation.

Neurogenic vasodilatation and plasma leakage in the skin

1. Primary afferent nerve fibers control cutaneous blood flow and vascular permeability by releasing vasoactive peptides. These vascular reactions and the additional recruitment of leukocytes are commonly embodied in the term neurogenic inflammation. 2. Calcitonin gene-related peptide (CGRP) acting via CGRP1 receptors is the principal transmitter of neurogenic dilatation of arterioles whereas substance P (SP) and neurokinin A (NKA) acting via NK1 receptors mediate the increase in venular permeability. 3. Neurogenic vasodilatation and plasma protein leakage play a role in inflammation because many inflammatory and immune mediators including interleukin-1 beta, nitric oxide, prostanoids, protons, bradykinin, histamine, and 5-hydroxytryptamine can stimulate peptidergic afferent nerve fibers or enhance their excitability. 4. Neurogenic inflammatory reactions can be suppressed by alpha 2-adrenoceptor agonists, histamine acting via H1 receptors, 5-hydroxytryptamine acting via 5-HT1B receptors, opioid peptides, and somatostatin through prejunctional inhibition of peptide release from vasoactive afferent nerve fibers. CGRP, SP, and NKA receptor antagonists are powerful pharmacological tools to inhibit neurogenic inflammation at the postjunctional level. 5. Imbalance between the facilitatory and inhibitory influences on afferent nerve activity has a bearing on chronic inflammatory disease. Impaired nerve function represents a deficit in skin homeostasis while neuronal overactivity is a factor in allergic and hyperreactive disorders of the skin.

Noradrenaline release from rat sympathetic neurones triggered by activation of B2 bradykinin receptors

1. The role of bradykinin receptors in the regulation of sympathetic transmitter release was investigated in primary cultures of neurones dissociated from superior cervical ganglia of neonatal rats. These cultures were loaded with [3H]-noradrenaline and the outflow of radioactivity was determined under continuous superfusion. 2. Bradykinin (100 nmol l[-1] applied for 10 min) caused a transient increase in tritium outflow that reached a peak within four minutes after the beginning of the application and then declined towards the baseline, despite the continuing presence of the peptide. ATP (100 micromol l[-1]) and nicotine (10 micromol l[-1]) caused elevations in 3H outflow with similar kinetics, whereas outflow remained elevated during a 10 min period of electrical field stimulation (0.5 ms, 50 mA, 50 V cm[-1], 1.0 Hz). 3. When bradykinin was applied for periods of 2 min, the evoked 3H overflow was half-maximal at 12 nmol l(-1) and reached a maximum of 2.3% of cellular radioactivity. The preferential B1 receptor agonist des-Arg9-bradykinin failed to alter 3H outflow. The B2 receptor antagonists, [D-Phe7]-bradykinin (1 micromol l[-1]) and Hoe 140 (10 nmol l[-1]), per se did not alter 3H outflow, but shifted the concentration-response curve for bradykinin-evoked 3H overflow to the right by a factor of 7.9 and 4.3, respectively. 4. Bradykinin-induced overflow was abolished in the absence of extracellular Ca2+ and in the presence of either 1 micromol l(-1) tetrodotoxin or 300 micromol l(-1) Cd2+, as was electrically-induced overflow. Activation of alpha2-adrenoceptors by 1 micromol l(-1) UK 14,304 reduced both bradykinin- and electrically-triggered overflow. The Ca2+-ATPase inhibitor thapsigargin (0.3 micromol l[-1]) failed to alter either type of stimulated overflow. Caffeine (10 mmol l[-1]) enhanced bradykinin-induced overflow, but reduced overflow triggered by electrical field stimulation. 5. Inclusion of Ba2+ (0.1 to 1 mmol l[-1]) in the superfusion medium enhanced electrically induced overflow by approximately 100% and potentiated bradykinin-triggered overflow by almost 400%. Application of 1 mmol l(-1) Ba2+ for periods of 2 min triggered 3H overflow, and this overflow was abolished by 1 micromol l(-1) tetrodotoxin and enhanced by 10 mmol l(-1) caffeine. In contrast, inclusion of tetraethylammonium (0.1 to 1 mmol l[-1]) in the superfusion buffer caused similar increases of bradykinin- and electrically evoked 3H overflow (by about 100%), and tetraethylammonium, when applied for 2 min, failed to alter 3H outflow. 6. Treatment of cultures with 100 ng ml(-1) pertussis toxin caused a significant increase in bradykinin-, but not in electrically-, evoked tritium overflow. Treatment with 100 ng ml(-1) cholera toxin reduced both types of stimulated 3H overflow. 7. These data reveal bradykinin as a potent stimulant of action potential-mediated and Ca2+-dependent transmitter release from rat sympathetic neurones in primary cell culture. This neurosecretory effect of bradykinin involves activation of B2-receptors, presumably linked to pertussis- and cholera toxin-insensitive G proteins, most likely members of the Gq family. Results obtained with inhibitors of muscarinic K+ (KM) channels, like caffeine and Ba2+, indicate that the secretagogue action of bradykinin probably involves inhibition of these K+ channels.

Peripheral pain mechanisms

Our understanding of the cellular and molecular bases of transduction of painful stimuli has burgeoned in the past year, mainly as a result of studies on isolated sensory neurones in culture. The ion channels underlying neuronal responses to noxious heat, to protons and to ATP have recently been characterized. The typical increase in nociceptor sensitivity produced by tissue damage has been found to be mediated by at least two distinct mechanisms. In the first, bradykinin augments the current activated by heat through a mechanism that involves activation of protein kinase C. In a second sensitization mechanism, prostaglandin E2 alters the voltage threshold of several ion channels, including a novel tetrodotoxin-insensitive Na+ channel, in such a way that initiation of action potentials is facilitated.

Pro-inflammatory effects induced by bradykinin in a murine model of pleurisy

Bradykinin caused a dose-related increase in cell influx 4 h after its administration into the mouse pleural cavity (ED50 = 3.2 nmol/cav., 95% confidence limits = 0.6-15.5). Cell influx peaked at 4 h and remained elevated for up to 72 h, whereas exudation was detected between 2 and 6 h after bradykinin administration. Both HOE 140 (D-Arg-[Hyp3,Thi5,D-Tic7, Oic8]bradykinin) and NPC 17731 (D-Arg0-[Hyp3 D-HypE(transpropyl7)Oic8]bradykinin) inhibited bradykinin-induced cell influx (ID50 0.028 (0.05-0.16) and 0.4 (0.3-0.7) pmol/cav., respectively). Des-Arg9-[Leu8]bradykinin (0.1 and 3.0 nmol/cav., 30 min before) did not inhibit the effects of bradykinin. Pre-treatment of animals with either indomethacin, terfenadine, dexamethasone, N(omega)-nitro-L-arginine benzyl ester, cromolyn, theophylline, salbutamol, FK 888 (N2-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl)carbonyl-L-propyl]N-met hyl-N-phenyl-methyl-3-(2-naphthyl)-L-alaninamide) or SR 142801 ((N)-(1-[3-[1-benzoyl-3-(3,4-dichloro-phenyl)-piperidin-3-yl]pr opy l]-4-phenyl-piperidin-4-yl)-N-methyl-acetamide) significantly inhibited cell migration (P < 0.01). These results indicate that bradykinin had a significant pro-inflammatory effect on the pleural cavity of the mice. This effect seems to be primarily mediated via activation bradykinin B2 receptors which trigger the release of other mediators.

Bradykinin receptors

1. The last decade has witnessed a phenomenal increase in our understanding of the pharmacology of bradykinin receptors, and has led to an appreciation of a key role for the peptide kinins as proinflammatory mediators. This short review summarises the major changes that have taken place in the expanding area of bradykinin receptor pharmacology, and highlights important advances that we hope to anticipate in the future. 2. Bradykinin receptors are cell surface, G-protein coupled receptors of the seven-transmembrane domained family. The existence of two subtypes of bradykinin receptor, B1 and B2, has been confirmed through the use of high affinity peptide and nonpeptide receptor antagonists, radioligand binding studies and, recently, receptor cloning and expression studies. 3. Differences in the affinities of B2 receptor antagonists, including those of the [D-Phe7]-bradykinin series, D-Arg-[Hyp3, Thi5, D-Tic7, Oic8]-bradykinin (Hoe140, Icatibant) and the non-peptide, WIN64338, have led to proposals of the possible existence of further subtypes of bradykinin receptor (including a tracheal B3 receptor), and/or of species homologues of the B2 receptor. 4. Molecular cloning techniques have identified the gene encoding B1 receptors in the rabbit, human and mouse, and B2 receptors in the rat, human and mouse. B1 and B2 receptor show little (36%) overall sequence homology. Cloning studies reveal the potential for the existence of species homologues of receptors. 5. The use of bradykinin receptor antagonists in vivo has led to an appreciation of the involvement of bradykinin receptors in inflammation. Evidence suggests a role for B2 receptors in more classical acute inflammatory events, such as oedema and inflammatory pain, whereas B1 receptors appear to be involved in chronic inflammatory responses, including certain forms of persistent hyperalgesia. 6. The continuing advances in our knowledge of the characteristics of bradykinin receptors through the further development of selective receptor antagonists and molecular biology techniques will aid in the rational design of drugs effective in the therapeutic manipulation of inflammatory processes and in the control of inflammatory disease.

A novel heat-activated current in nociceptive neurons and its sensitization by bradykinin

Pain differs from other sensations in many respects. Primary pain-sensitive neurons respond to a wide variety of noxious stimuli, in contrast to the relatively specific responses characteristic of other sensory systems, and the response is often observed to sensitize on repeated presentation of a painful stimulus, while adaptation is typically observed in other sensory systems. In most cases the cellular mechanisms of transduction and sensitization in response to painful stimuli are not understood. We report here that application of pulses of noxious heat to a subpopulation of isolated primary sensory neurons rapidly activates an inward current. The ion channel activated by heat discriminates poorly among alkali cations. Calcium ions both carry current and partially suppress the current carried by other ions. The current is markedly increased by bradykinin, a potent algogenic nonapeptide that is known to be released in vivo by tissue damage. Phosphatase inhibitors prolong the sensitization caused by bradykinin, and a similar sensitization is caused by activators of protein kinase C. We conclude that bradykinin sensitizes the response to heat by activating protein kinase C.