The role of an alpha-selective phosphoinositide-3 kinase inhibitor in vascular inflammation

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): British Heart Foundation

Introduction

Cardiovascular inflammation is associated with endothelial cell (EC) damage, resulting in leukocyte trafficking and oedema formation. Inflammation disrupts EC junctions, increasing microvascular permeability, and resulting in a positive-feedback loop of inflammatory events. The phosphoinositide 3-kinase pathway stimulates this endothelial response and this study examined the actions of BYL-719, a PI3K-α selective inhibitor, on inflammatory responses.

Method

Confocal imaging using immunofluorescence and permeability assays were undertaken to quantify the effect of inflammatory cytokines, TNF-α and IL-1β, in the presence of the PI3K inhibitor using fluorescein isothiocyanate-dextran (40 kDa, 0.1 mg/ml) on human microvascular endothelial cells (HMVEC) (Lonza, derived from dermal tissue). Cells were treated with either cytokine for 16-18 h, followed by a 1 h treatment of drug and a final 1 h treatment with FITC-dextran. In vivo analysis was carried out per the UK Home Office Animals (Scientific Procedures) Act 1986. Male WT CD1 mice were anaesthetised initially using 5% isoflurane and maintained at 2% for procedures, to test BYL-719 in a model of dorsal skin inflammation, to determine neutrophil accumulation (measured by myeloperoxidase) and oedema formation (measured by Evans Blue accumulation). All statistical significance was determined using one-way or two-way ANOVA followed by Tukey’s post hoc test.

Results

BYL-719 significantly reduced cytokine-induced EC permeability and shape changes, including cell area and elongation (Table 1), impeding in vitro cytokine-induced inflammation. The inhibitor, abrogated effects of the inflammatory cytokines in vivo of both TNF-α and IL-1β, but interestingly had no effect on the neutrophil accumulation or oedema formation in the presence of C5a (Figure 1).

Figure 1: The effect of BYL-719 in the dorsal skin inflammation model. Mice were pre-treated with 50 mg/kg BYL-719 intraperitoneally for 30 min, injected intravenously with Evans Blue dye, intradermally injected with TNF-α (100ng/50ul), IL-1β (10ng/50ul) and C5a (300ng/50ul) for 4 h, followed by ex vivo MPO assay (A) and oedema volume measurements (B). Data are mean ±SEM two-way ANOVA by Tukey test., n=6 independent experiments in duplicates; p* < 0.05 and p**** < 0.0001 between control (DMSO) and BYL-719 treated groups.

Conclusions

Our findings show that the PI3K-α inhibitor, BYL-719, reduces endothelial activation and inhibits inflammatory oedema formation in the presence of TNF-α and IL-1β. We conclude that there is a potential for PI3K inhibitors to act as anti-neutrophil and oedema agents in cardiovascular-related inflammatory conditions.

Calcitonin Gene-Related Peptide Protects Against Cardiovascular Dysfunction Independently of Nitric Oxide In Vivo

[Figure: see text].

P701The role of a phosphoinositide-3 kinase inhibitor in vascular inflammation

Background/Introduction

Cardiovascular inflammation is associated with endothelial damage, resulting in leukocyte trafficking and oedema formation, which results in a positive-feedback loop of inflammatory events.

Purpose

The phosphoinositide 3-kinase (PI3K) pathway has been shown to be upregulated in vascular disease conditions whereby its inhibitors potentially have beneficial effects. Hence this study was designed to examine the actions of PI-103, a PI3K non-selective inhibitor, on inflammatory responses.

Methods

Permeability assays were undertaken to quantify the effect of TNF-a in the presence and absence of PI-103 using FITC-dextran (40 kDa, 0.1 mg/ml) to measure levels of permeability in trans-wells plates using human microvascular endothelial cells (HMVEC).

In vivo analysis was carried out per the UK Home Office Animals (Scientific Procedures) Act 1986. CD1 mice were anaesthetised, to test PI-103 in a zymosan-induced model of dorsal skin inflammation on neutrophil accumulation (measured by myeloperoxidase) and oedema formation (measured by Evans Blue accumulation).

All data were analysed using 1-way or 2-way ANOVA with post-hoc test.

Results

PI-103 significantly reduced TNF-α induced microvascular endothelial cell permeability (Graph), thus impeding in vitro cytokine-induced inflammation. Whilst there was no effect on neutrophil accumulation in vivo, there was significant reduction in weight of treated areas and oedema formation, which was inhibited by PI-103 (Table 1).

Effect of PI-103 in vivo Control 30 mg/kg PI-103 Tyrode solution Zymosan (μg/ml) Tyrode solution Zymosan (μg/ml) 10 30 100 10 30 100 MPO/Protein (U/mg) 0.66±0.26 1.42±0.07 1.40±0.14 1.68±0.12* 0.60±0.11 1.23±0.32 1.36±0.25 1.59±0.21* Oedema Volume (mm3) 0.00±0.00 3.26±1.76 11.70±2.21 21.50±4.67 2.20±1.53 1.05±1.05 3.27±0.74 5.52±1.58 Mice were pre-treated with PI-103 i.p. for 30 min, i.d injected with zymosan (50 μl/site) for 4 hr, followed by ex vivo MPO assay, weight and oedema volume measurements. Oedema was quantified by measuring: width (x), height (y) and depth (z) from each of the i.d. sites; volume of oedema = ((π/6)xyz). N=6 independent experiments in duplicates; *p<0.05 between Tyrode solution vs zymosan groups.

Effect of PI103 in vitro on permeability

Conclusions

Our findings show that the PI3K non-selective inhibitor, PI-103 (as well as a PI3K α-selective inhibitor), reduces endothelial activation and inhibits inflammatory oedema formation. We conclude that there is a potential for PI3K inhibitors to act as anti-oedema agents in cardiovascular-related inflammatory conditions.

Acknowledgement/Funding

British Heart Foundation

Evidence for physiological and pathological roles for sensory nerves in the microvasculature and skin

This review highlights the progress from the initial finding of neurogenic inflammation up to the most recent development in the field of sensory nerves research, focusing on their roles in the microvasculature and the skin. Recent discovery of Transient Receptor Potential (TRP) channels highlight their important roles in detecting a range of environmental stimuli, including chemical and temperature. This provides us novel mechanisms for driving neurogenic inflammation upstream of neuropeptide release in addition to promising potential therapeutic targets in various diseases, including pain, itching and skin inflammation.

Calcitonin gene-related peptide: physiology and pathophysiology

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide. Discovered 30 years ago, it is produced as a consequence of alternative RNA processing of the calcitonin gene. CGRP has two major forms (α and β). It belongs to a group of peptides that all act on an unusual receptor family. These receptors consist of calcitonin receptor-like receptor (CLR) linked to an essential receptor activity modifying protein (RAMP) that is necessary for full functionality. CGRP is a highly potent vasodilator and, partly as a consequence, possesses protective mechanisms that are important for physiological and pathological conditions involving the cardiovascular system and wound healing. CGRP is primarily released from sensory nerves and thus is implicated in pain pathways. The proven ability of CGRP antagonists to alleviate migraine has been of most interest in terms of drug development, and knowledge to date concerning this potential therapeutic area is discussed. Other areas covered, where there is less information known on CGRP, include arthritis, skin conditions, diabetes, and obesity. It is concluded that CGRP is an important peptide in mammalian biology, but it is too early at present to know if new medicines for disease treatment will emerge from our knowledge concerning this molecule.

Regulation of alternative VEGF-A mRNA splicing is a therapeutic target for analgesia

Vascular endothelial growth factor-A (VEGF-A) is best known as a key regulator of the formation of new blood vessels. Neutralization of VEGF-A with anti-VEGF therapy e.g. bevacizumab, can be painful, and this is hypothesized to result from a loss of VEGF-A-mediated neuroprotection. The multiple vegf-a gene products consist of two alternatively spliced families, typified by VEGF-A₁₆₅a and VEGF-A₁₆₅b (both contain 165 amino acids), both of which are neuroprotective. Under pathological conditions, such as in inflammation and cancer, the pro-angiogenic VEGF-A₁₆₅a is upregulated and predominates over the VEGF-A₁₆₅b isoform.

We show here that in rats and mice VEGF-A₁₆₅a and VEGF-A₁₆₅b have opposing effects on pain, and that blocking the proximal splicing event – leading to the preferential expression of VEGF-A₁₆₅b over VEGF₁₆₅a – prevents pain in vivo. VEGF-A₁₆₅a sensitizes peripheral nociceptive neurons through actions on VEGFR2 and a TRPV1-dependent mechanism, thus enhancing nociceptive signaling. VEGF-A₁₆₅b blocks the effect of VEGF-A₁₆₅a.

After nerve injury, the endogenous balance of VEGF-A isoforms switches to greater expression of VEGF-A_xxxa compared to VEGF-A_xxxb, through an SRPK1-dependent pre-mRNA splicing mechanism. Pharmacological inhibition of SRPK1 after traumatic nerve injury selectively reduced VEGF-A_xxxa expression and reversed associated neuropathic pain. Exogenous VEGF-A₁₆₅b also ameliorated neuropathic pain.

We conclude that the relative levels of alternatively spliced VEGF-A isoforms are critical for pain modulation under both normal conditions and in sensory neuropathy. Altering VEGF-A_xxxa/VEGF-A_xxxb balance by targeting alternative RNA splicing may be a new analgesic strategy.

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The different vegf-a splice variants, VEGF-A₁₆₅a and VEGF-A₁₆₅b have pro- and anti-nociceptive actions respectively.

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Pro-nociceptive actions of VEGF-A₁₆₅a are dependent on TRPV1.

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Alternative pre-mRNA splicing underpins peripheral sensitization by VEGF-A isoforms in normal and neuropathic animals.

Transient receptor potential ankyrin 1: emerging pharmacology and indications for cardiovascular biology

Transient receptor potential anykrin 1 (TRPA1) is a member of the TRP superfamily, representing the sole member of the TRPA subfamily. It has many identified endogenous and exogenous agonists, comprising largely of chemical irritants and products of oxidative stress. Classically located on sensory neurone endings, TRPA1 has developed a strong presence in pain and inflammatory studies, where it is now becoming an intriguing clinical drug target. TRPA1 is increasingly recognized in a growing number of neuronal and non-neuronal locations with expanding expression and activity profiles providing evidence of a role for TRPA1 in other systems. Interest in discovering the pharmacological and functional roles of TRPA1 is increasing and diversifying into many areas. Historically, compounds now known as TRPA1 agonists have demonstrated cardiovascular activity, modulating activities in both the heart and the vasculature. Now TRPA1 has been identified as the receptor via which these compounds can act, these studies are being revisited and expanded on using current techniques. It is therefore timely to review the current knowledge of TRPA1 receptor presence and activities of relevance to the cardiovascular system, summarizing findings to date and identifying potential areas for future investigation.

A role for the medial preoptic area in CGRP-induced suppression of pulsatile LH secretion in the female rat

Calcitonin gene-related peptide (CGRP) is involved in a variety of stress responses and plays a pivotal role in stress-induced suppression of the GnRH pulse generator in the rat. Intracerebroventricular administration of CGRP suppresses luteinizing hormone (LH) pulses and increases Fos expression within the medial preoptic area (mPOA) and paraventricular nucleus (PVN). The aims of the present study were to investigate whether the mPOA or PVN are sites of action for CGRP-induced suppression of LH pulses and whether lipopolysaccharide (LPS), restraint or insulin-induced hypoglycaemia, stressors known to suppress LH pulses, affect mRNA expression for CGRP and its receptor subunits (calcitonin receptor-like receptor (CL) and RAMP-1) in the mPOA and PVN. Micro-infusion of CGRP (50, 250 or 500 pmol) into the mPOA, but not the PVN, dose-dependently suppressed LH pulse frequency. LPS, restraint and hypoglycaemia suppressed RAMP-1 mRNA, but not CL or CGRP mRNA expression in the mPOA. In the PVN, all three stressors suppressed CL mRNA expression, but only LPS or restraint suppressed RAMP-1 mRNA, and CGRP mRNA was unaffected. These results provide evidence that, unlike the PVN, the mPOA might play an important role in the inhibitory effect of CGRP on pulsatile LH secretion. Additionally, CGRP receptor function may be involved in this brain region in stress-induced suppression of the GnRH pulse generator.

Hydrogen peroxide is a novel mediator of inflammatory hyperalgesia, acting via transient receptor potential vanilloid 1-dependent and independent mechanisms

Inflammatory diseases associated with pain are often difficult to treat in the clinic due to insufficient understanding of the nociceptive pathways involved. Recently, there has been considerable interest in the role of reactive oxygen species (ROS) in inflammatory disease, but little is known of the role of hydrogen peroxide (H(2)O(2)) in hyperalgesia. In the present study, intraplantar injection of H(2)O(2)-induced a significant dose- and time-dependent mechanical and thermal hyperalgesia in the mouse hind paw, with increased c-fos activity observed in the dorsal horn of the spinal cord. H(2)O(2) also induced significant nociceptive behavior such as increased paw licking and decreased body liftings. H(2)O(2) levels were significantly raised in the carrageenan-induced hind paw inflammation model, showing that this ROS is produced endogenously in a model of inflammation. Moreover, superoxide dismutase and catalase significantly reduced carrageenan-induced mechanical and thermal hyperalgesia, providing evidence of a functionally significant endogenous role. Thermal, but not mechanical, hyperalgesia in response to H(2)O(2) (i.pl.) was longer lasting in TRPV1 wild type mice compared to TRPV1 knockouts. It is unlikely that downstream lipid peroxidation was increased by H(2)O(2). In conclusion, we demonstrate a notable effect of H(2)O(2) in mediating inflammatory hyperalgesia, thus highlighting H(2)O(2) removal as a novel therapeutic target for anti-hyperalgesic drugs in the clinic.

The role of corticotrophin-releasing hormone receptors in the calcitonin gene-related peptide-induced suppression of pulsatile luteinising hormone secretion in the female rat

Corticotrophin-releasing hormone (CRH) plays a pivotal role in the suppression of the gonadotrophin-releasing hormone (GRH) pulse generator in response to stress and intracerebroventricular (i.c.v.) administration of calcitonin gene-related peptide (CGRP). We have previously shown both CRH receptor subtypes, CRH-R1 and CRH-R2, are involved in the stress-induced suppression of LH pulses. The aims of the present study were to examine the role of CRH-R1 and CRH-R2 in CGRP-induced suppression of LH pulses, and to investigate the effects of CGRP on CRH expression in the paraventricular nucleus (PVN) and central nucleus of the amygdala (CeA), which have prominent CRH neurone populations that receive dense CGRP innervations. The suppression of LH pulses by CGRP (1.5 microg i.c.v.) was completely prevented by intravenous administration of the CRH-R1 antagonist SSR125543Q (7.5 mg/rat i.v., 30 min before CGRP), but was not affected by the CRH-R2 antagonist, astressin(2)-B (100 microg i.c.v., 10 min before CGRP). CGRP increased the CRH mRNA expression in PVN and CeA. These results provide evidence of a role for CRH-R1 in mediating the suppressive effects of CGRP on pulsatile LH secretion in the female rat, and additionally raise the possibility of an involvement of PVN and CeA CRH neuronal populations in this suppression.

Evidence for the role of neurogenic inflammation components in trypsin-elicited scratching behaviour in mice

BACKGROUND AND PURPOSE

We investigated the mechanisms underlying the pruritogenic response induced by trypsin in mice, to assess the relevance of neurogenic inflammation components in this response.

EXPERIMENTAL APPROACH

Itching was induced by an intradermal injection of trypsin in the mouse neck. The animals were observed for 40 min and their scratching behaviour was quantified.

KEY RESULTS

Trypsin-induced itching was blocked by the lima bean trypsin inhibitor, the selective proteinase-activated receptor-2 (PAR-2) antagonist FSLLRY and PAR-2 receptor desensitization. An important involvement of mast cells was observed, as chronic pretreatment with the mast cell degranulator compound 48/80 or the mast cell stabilizer disodium cromoglycate prevented scratching. Also, trypsin response was inhibited by the selective COX-2 inhibitor celecoxib and by the selective kinin B2 (FR173657) and B1 (SSR240612) receptor antagonists. Moreover, an essential role for the mediators of neurogenic inflammation was established, as the selective NK1 (FK888), NK3 (SR142801) and calcitonin gene-related peptide (CGRP(8-37) fragment) receptor antagonists inhibited trypsin-induced itching. Similarly, blockade of transient receptor potential vanilloid 1 (TRPV1) receptors by the selective TRPV1 receptor antagonist SB366791, or by genetic deletion of TRPV1 receptor reduced this behaviour in mice. C-fibre desensitization showed a very similar result.

CONCLUSIONS AND IMPLICATIONS

Trypsin intradermal injection proved to be a reproducible model for the study of itching and the involvement of PAR-2 receptors. Also, trypsin-induced itching seems to be widely dependent on neurogenic inflammation, with a role for TRPV1 receptors. In addition, several other mediators located in the sensory nerves and skin also seem to contribute to this process.

Neonatal lipopolysaccharide exposure exacerbates stress-induced suppression of luteinizing hormone pulse frequency in adulthood

Early life exposure to immunological challenge has programming effects on the adult hypothalamo-pituitary-adrenocortical axis stress responsivity, and stress is known to suppress GnRH pulse generator activity, especially LH pulses. We investigated the effects of neonatal exposure to endotoxin on stress-induced suppression of pulsatile LH secretion and the involvement of corticotropin-releasing factor (CRF) receptor mechanisms in adult rats. Pups at 3 and 5 d of age were administered lipopolysaccharide (LPS, 50 microg/kg, ip). At 12 wk of age, they were ovariectomized and implanted with sc 17beta-estradiol capsules and i.v. cannulas. Blood samples (25 microl) were collected every 5 min for 5 h for LH measurement. After 2 h of sampling, rats were given LPS (25 microg/kg, iv). CRF and CRF-R1 and CRF-R2 receptor mRNA was determined by RT-PCR in medial preoptic area (mPOA) micropunches collected at 3 h after LPS administration. There was no difference in basal LH pulse frequency between neonatal LPS- and neonatal saline-treated controls. However, neonatal endotoxin-treated rats exhibited a significantly greater LPS stress-induced suppression of LH pulse frequency. Basal mPOA CRF-R1 expression was unchanged in neonatal LPS- and neonatal saline-treated rats. However, CRF-R1 expression was significantly increased in response to LPS stress in neonatal LPS-treated animals but not in neonatal saline-treated controls. CRF and CRF-R2 expression was unchanged in all treatment groups. These data demonstrate that exposure to bacterial endotoxin in early neonatal life programs long-term sensitization of the GnRH pulse generator to the inhibitory influence of stress in adulthood, an effect that might involve up-regulation of CRF-R1 expression in the mPOA.

Differential role of corticotrophin-releasing factor receptor types 1 and 2 in stress-induced suppression of pulsatile luteinising hormone secretion in the female rat

Corticotrophin-releasing factor (CRF) plays a pivotal role in stress-induced suppression of the gonadotrophin-releasing hormone pulse generator. We have previously shown that type 2 CRF receptors (CRF(2)) mediate restraint stress-induced suppression of luteinising hormone (LH) pulses in the rat. The present study aimed: (i) to determine whether type 1 CRF receptors (CRF(1)) are also involved in this response to restraint and (ii) to investigate the differential involvement of CRF(1) and CRF(2) in the suppression of LH pulses in response to the metabolic perturbation of insulin-induced hypoglycemia and the innate immunological challenge of lipopolysaccharide (LPS). Ovariectomised rats with oestrogen replacement were implanted with intracerebroventricular (i.c.v.) and intravenous (i.v.) cannulae. Blood samples (25 microl) were collected every 5 min for 5 h for LH measurement. After 2 h of controlled blood sampling, rats were either exposed to restraint (1 h) or injected intravenously with insulin (0.25 IU/kg) or LPS (5 microg/kg). All three stressors suppressed LH pulses. The CRF(1) antagonist SSR125543Q (11.5 micromol/rat i.v., 30 min before stressor) blocked the inhibitory response to restraint, but not hypoglycaemia or LPS stress. In addition to its effect on restraint, the CRF(2) antagonist astressin(2)-B (28 nmol/rat i.c.v., 10 min before insulin or LPS) blocked hypoglycaemia or LPS stress-induced suppression of LH pulses. These results suggest that hypoglycaemia and LPS stress-induced LH suppression involves activation of CRF(2) while restraint stress-induced inhibition of LH pulses involves both CRF(1) and CRF(2).

Neutrophils in development of multiple organ failure in sepsis

Multiple organ failure is a major threat to the survival of patients with sepsis and systemic inflammation. In the UK and in the USA, mortality rates are currently comparable with and projected to exceed those from myocardial infarction. The immune system combats microbial infections but, in severe sepsis, its untoward activity seems to contribute to organ dysfunction. In this Review we propose that an inappropriate activation and positioning of neutrophils within the microvasculature contributes to the pathological manifestations of multiple organ failure. We further suggest that targeting neutrophils and their interactions with blood vessel walls could be a worthwhile therapeutic strategy for sepsis.

Capsaicin-induced vasoconstriction in the mouse knee joint: a study using TRPV1 knockout mice

Capsaicin is the pungent component of chilli peppers that concomitantly activates and desensitizes C-fibre and Adelta sensory nerve fibres. Stimulation causes an acute neurogenic response including vasodilation, plasma extravasation and hypersensitivity. However, in the present study we have shown that capsaicin produces a dose-dependent vasoconstrictor effect in the mouse knee joint via Transient Receptor Potential Vanilloid 1 (TRPV1) receptor activation. A (125)I-albumin accumulation technique showed that the intravascular volume of capsaicin-treated joints in wild type (WT) mice was significantly reduced compared to TRPV1 knockout mice (p<0.01). Similarly, a laser Doppler technique showed significantly reduced blood flow in the capsaicin-treated joints of WT compared to TRPV1 knockout mice (p<0.001). Pretreatment with guanethinidine (50 mg kg(-1), i.p.) had no effect on the vasoconstriction. These data are important considering the involvement of TRPV1 receptors in joint disease. The mechanisms underlying the vasoconstriction therefore require further investigation.

Enhanced Vascular Responses to Adrenomedullin in Mice Overexpressing Receptor-Activity–Modifying Protein 2

Adrenomedullin (AM) levels are elevated in cardiovascular disease, but little is known of the role of specific receptor components. AM acts via the calcitonin receptor-like receptor (CLR) interacting with a receptor-activity–modifying protein (RAMP). The AM 1 receptor is composed of CLR and RAMP2, and the calcitonin gene–related peptide (CGRP) receptor of CLR and RAMP1, as determined by molecular and cell-based analysis. This study examines the relevance of RAMP2 in vivo. Transgenic (TG) mice that overexpress RAMP2 in smooth muscle were generated. The role of RAMP2 in the regulation of blood pressure and in vascular function was investigated. Basal blood pressure, acute angiotensin II–raised blood pressure, and cardiovascular properties were similar in wild-type (WT) and TG mice. However, the hypotensive effect of IV AM, unlike CGRP, was enhanced in TG mice ( P <0.05), whereas a negative inotropic action was excluded by left-ventricular pressure–volume analysis. In aorta relaxation studies, TG vessels responded in a more sensitive manner to AM (EC 50 , 8.0±1.5 nmol/L) than WT (EC 50 , 17.9±3.6 nmol/L). These responses were attenuated by the AM receptor antagonist, AM 22-52 , such that residual responses were identical in all mice. Remaining relaxations were further inhibited by CGRP receptor antagonists, although neither affected AM responses when given alone. Mesenteric and cutaneous resistance vessels were also more sensitive to AM in TG than WT mice. Thus RAMP2 plays a key role in the sensitivity and potency of AM-induced hypotensive responses via the AM 1 receptor, providing evidence that this receptor is a selective target for novel therapeutic approaches.

Effect of calcitonin gene-related peptide on gonadotrophin-releasing hormone mRNA expression in GT1-7 cells

Recent evidence has shown calcitonin gene-related peptide (CGRP) to be a key mediator of stress-induced suppression of the gonadotrophin-releasing hormone (GnRH) pulse generator, although little is known about the neural pathways involved. In the present study, we investigated the potential direct action of CGRP on GnRH neurones using GT1-7 cells, an established GnRH cell line. First, we detected expression of the CGRP receptor subunits, calcitonin receptor-like receptor and receptor activity-modifying protein-1 in the GT1-7 cells by reverse transcriptase-polymerase chain reaction. Second, we have shown that CGRP inhibits GnRH mRNA expression in the GT1-7 cells, which was effectively reversed by the CGRP receptor antagonist, CGRP8-37. These results suggest that CGRP down regulates expression of GnRH mRNA, via CGRP receptors in the GT1-7 cell, thus implying that a potential direct action of CGRP may mediate a suppressive effect on the GnRH neural network.

The role of substance P in microvascular responses in murine joint inflammation

1. Rheumatoid arthritis is a serious, inflammatory disease of the distal joints that has a possible neurogenic component underlying its pathology. 2. Substance P (SP), an endogenous neuropeptide that acts upon the neurokinin 1 (NK(1)) receptor, is released from sensory nerves and is involved in neurogenic inflammation. 3. In this study, we have developed novel techniques to determine the contribution of SP to microvascular responses in a model of complete Freund's adjuvant (CFA)-induced arthritis in NK(1) knockout mice. 4. Detailed analysis in normal mice revealed that CFA (20 microg i.art.)-induced plasma extravasation was raised from 18 to 72 h, when compared with intravascular volume. By comparison, knee swelling was sustained for 3 weeks. Neutrophil accumulation mirrored plasma extravasation. SP (10 pmol i.art.) caused significant acute plasma extravasation, but not other parameters, in wild type (WT), but not NK(1) knockout mice. CFA (10 microg i.art.) induced a significantly decreased intravascular volume, presumably due to decreased blood flow, at early time points (5 and 7 h) in WT but not NK(1) knockouts. Otherwise, similar responses in WT and NK(1) knockout mice were observed. However, injection of SP into CFA-pretreated joints caused a significant enhancement of plasma extravasation and knee swelling in the WT but not NK(1) knockouts. 5. In conclusion, the present study has used novel techniques in WT and NK(1) knockout mice to show that SP can modulate vascular tone and permeability in the inflamed joint via activation of the NK(1) receptor and that SP-induced responses are more pronounced where pre-existing inflammation is present.

Calcitonin gene-related peptide-induced suppression of luteinizing hormone pulses in the rat: the role of endogenous opioid peptides

Calcitonin gene-related peptide (CGRP) is involved in a variety of stress responses in the rat. Central administration of CGRP activates the hypothalamo-pituitary-adrenal axis resulting in increased corticosterone secretion. We have previously shown that central CGRP suppresses the gonadotrophin-releasing hormone (GnRH) pulse generator, specifically LH pulses. Endogenous opioid peptides (EOPs) have been shown to play an important role in stress-induced suppression of the reproductive axis. The aim of the present study was to test the hypothesis that EOPs mediate CGRP-induced suppression of pulsatile LH secretion. Ovariectomized rats were implanted with intracerebroventricular (i.c.v.) and i.v. cannulae. Intravenous administration of the opioid antagonist naloxone (250 microg) completely blocked the suppression of LH pulses induced by 1.5 microg i.c.v. CGRP and significantly attenuated the suppression of pulsatile LH secretion induced by 5 microg i.c.v. CGRP. Furthermore, intravenous administration of naloxone was found to immediately restore normal LH pulse frequency in animals treated 90 min earlier with 1.5 microg i.c.v. CGRP. Co-administration (i.c.v.) of CGRP (1.5 microg) with the mu and kappa opioid receptor-specific antagonists naloxone (10 microg) and norbinaltorphimine (5 microg), respectively, blocked the CGRP-induced suppression of LH pulses, whilst i.c.v. co-administration of CGRP (1.5 microg) with the delta opioid receptor-specific antagonist naltrindole (5 microg) did not. These data provide evidence that EOPs play a pivotal role in mediating the inhibitory effects of CGRP on pulsatile LH secretion in the rat. They also suggest that the mu and kappa, but not the delta, opioid receptors may be responsible for mediating the effects of CGRP on LH pulses.

A role for substance P in arthritis?

Substance P is a neuropeptide that is released from sensory nerves and which has a number of pro-inflammatory effects. In this article, we review the evidence for a role of substance P in arthritis, both in experimental animal models and rheumatoid arthritis patients. Substance P expression is altered in the joint and dorsal horn of arthritic animals, exogenous substance P and neurokinin 1 (NK(1)) receptor antagonists modulate responses in the joint, and there is some evidence for a role of substance P in human joint disease. However, the therapeutic potential of NK(1) receptor antagonists in the treatment of rheumatoid arthritis remains controversial.

The calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS blocks CGRP and adrenomedullin vasoactive responses in the microvasculature

Calcitonin gene-related peptide (CGRP) is a potent microvascular dilator neuropeptide that is considered to play an essential role in neurogenic vasodilatation and in maintaining functional integrity in peripheral tissues. We have examined the effect of the nonpeptide CGRP antagonist BIBN4096BS on responses to CGRP and the structurally related peptide adrenomedullin, AM, in murine isolated aorta and mesentery preparations, and in the cutaneous microvasculature in vivo. We show for the first time that BIBN4096BS is an effective antagonist of CGRP and AM responses in the murine mesenteric and cutaneous microvasculature, and of CGRP in the murine aorta. After local administration, BIBN4096BS selectively inhibits the potentiation of microvascular permeability in the cutaneous microvasculature by CGRP and AM, with no effect on responses induced by other microvascular vasodilators. BIBN4096BS reversed both newly developed and established vasoactive responses induced by CGRP. The ability of CGRP to potentiate plasma extravasation was lost when coinjected with compound 48/80 (where mast cells would be activated to release proteases), but regained when soybean trypsin inhibitor was coinjected with compound 48/80. These results demonstrate that BIBN4096BS is a selective antagonist of responses induced by CGRP and AM in the mouse microvasculature, and CGRP in the mouse aorta. The ability of BIBN4096BS to block an established CGRP microvascular vasodilatation indicates that the sustained vasodilator activity of CGRP is due to the retention of the active intact peptide and the continued involvement of the CGRP receptor.

Mustard oil induces a transient receptor potential vanilloid 1 receptor-independent neurogenic inflammation and a non-neurogenic cellular inflammatory component in mice

A neurogenic component has been suggested to play a pivotal role in a range of inflammatory/immune diseases. Mustard oil (allyl-isothiocyanate) has been used in studies of inflammation to mediate neurogenic vasodilatation and oedema in rodent skin. The aim of the present study was to analyse mustard oil-induced oedema and neutrophil accumulation in the mouse ear focussing on the roles of neurokinin 1 (NK(1)) and vanilloid (TRPV1) receptors using normal (BALB/c, C57BL/6) as well as NK(1) and TRPV1 receptor knockout mice. A single or double treatment of 1% mustard oil on the BALB/c mouse ear induced ear oedema with responses diminished by 6 h. However a 25-30% increase in ear thickness was maintained by the hourly reapplication of mustard oil. Desensitisation of sensory nerves with capsaicin, or the NK(1) receptor antagonist SR140333, inhibited oedema but only in the first 3 h. Neutrophil accumulation in response to mustard oil was inhibited neither by SR140333 nor capsaicin pre-treatment. An activating dose of capsaicin (2.5%) induced a large oedema in C57BL/6 wild-type mice that was minimal in TRPV1 receptor knockout mice. By comparison, mustard oil generated ear swelling was inhibited by SR140333 in wild-type and TRPV1 knockout mice. Repeated administration of mustard oil maintained 35% oedema in TRPV1 knockout animals and the lack of TRPV1 receptors did not alter the leukocyte accumulation. In contrast repeated treatment caused about 20% ear oedema in Sv129+C57BL/6 wild-type mice but the absence of NK(1) receptors significantly decreased the response. Neutrophil accumulation showed similar values in both groups. This study has revealed that mustard oil can act via both neurogenic and non-neurogenic mechanisms to mediate inflammation in the mouse ear. Importantly, the activation of the sensory nerves was still observed in TRPV1 knockout mice indicating that the neurogenic inflammatory component occurs via a TRPV1 receptor independent process.

Protein nitration in cutaneous inflammation in the rat: essential role of inducible nitric oxide synthase and polymorphonuclear leukocytes

1: We have examined the relationship between neutrophil accumulation, NO(*) production and nitrated protein levels in zymosan-mediated inflammation in rat skin in vivo. 2: Rats were anaesthetized and cutaneous inflammation was induced by zymosan (injected intradermally, i.d.). Experiments were carried out up to 48 h, in recovery procedures as appropriate. Assays for neutrophil accumulation (measurement of myeloperoxidase), nitric oxide (assessment of NO(2)(-)/NO(3)(-)) and nitrated proteins (detected by ELISA and Western blot) were performed in skin extracts. 3: The results demonstrate a close temporal relationship between these parameters. Samples were assayed at 1, 4, 8, 24 and 48 h after i.d. injection of zymosan. The highest levels measured of each parameter (P<0.001 compared with vehicle) were found at 4-8 h, with a reduction towards basal levels by 24 h. 4: Selective depletion of circulating neutrophils with anti-neutrophil antibody abolished neutrophil accumulation and protein nitration. In addition substantially decreased NO levels were found. 5: A selective inducible nitric oxide synthase (iNOS) inhibitor, N-3-aminomethyl-benzyl-acetamidine-dihydrochloride (1400W) also significantly reduced neutrophil levels and NO production and substantially inhibited protein nitration. 6: We conclude that the neutrophil leukocyte plays an essential role in the formation of iNOS-derived NO and nitrated proteins in inflammation, in a time-dependent and reversible manner. The NO-derived iNOS also has a role in stimulating further neutrophil accumulation into skin. This suggests a close mechanistic coupling between neutrophils, NO production and protein nitration.

B1 and B2 antagonists and bradykinin-induced blood flow in rat skin inflammation

OBJECTIVE AND DESIGN

The aim of the present study was to examine the contribution of the two kinin receptors B1 and B2 to the increased blood flow observed in response to bradykinin (BK) in a blister model under different injury conditions.

MATERIAL

Young male Sprague-Dawley rats weighing 250-350 g were used.

METHODS

A vacuum-induced blister was raised in the rat hind paw and blood flow measured in the superfused blister base under four different conditions including, early phase acute injury; late phase acute injury; recurrent injury and early phase acute injury in the setting of chronic nerve damage. BK (10 microM) was superfused alone, or in the presence of the B1 antagonist DesArg9Leu8BK (DALBK), (10 nM) and/or the B2 antagonist [D-Arg,Hyp3,Thi5 D-Tic7,Oic8] Bradykinin (HOE 140) (10 nM).

RESULTS

HOE 140 significantly inhibited the BK response in all models. Significant inhibition of BK-induced vasodilatation by DALBK was only observed in the late phase acute and recurrent injury models.

CONCLUSIONS

The results suggest that the involvement of the inducible B1 receptor in skin inflammation site is related to the site, duration and recurrence of the injury condition.

Lack of a significant effect of deletion of the tachykinin neurokinin-1 receptor on wound healing in mouse skin

The tachykinin neurokinin-1 (NK(1)) receptor mediates the vasoactive effects of substance P and related members of the tachykinin family. Substance P acts via the NK(1) receptor to mediate increased microvascular permeability leading to oedema formation as confirmed in NK(1) receptor knockout mice. In addition there is evidence that neuropeptides such as substance P can have a modulatory effect on the wound-healing process. In this study male and female wild-type and NK(1) knockout mice were investigated for their comparative ability to induce acute oedema formation in response to topical application of capsaicin, as measured by the extravasation of intravenous radiolabelled-albumin, and wound healing in response to a cut, as measured by area of wound over the following days. Significant (P<0.001) oedema, approximately three-fold over basal, was induced by capsaicin in both male and female wild-type mice, an indicator of a similar responsiveness irrespective of sex. However, as expected, the oedema was not observed in the knockout mice. Wounding was achieved through a 1-cm full-thickness cut into the interscapular area of dorsal skin. Wound healing was then followed in two different protocols. The wound was left to heal naturally over 14 days in the first protocol and no significant changes in healing were observed in wild-type compared to knockout. In the second protocol, the skin was sutured open for the first 48 h, to prevent the elasticity of the skin from initiating a natural healing process through flap formation. This caused a significant increase in the area of the wound. Despite this, wounds in both wild-type and knockout mice healed in an identical manner that was complete after 17 days. In conclusion, it is shown that deletion of a functional NK(1) receptor has little effect on wound healing in response to a simple cut in mouse skin.

Studies of the microvascular effects of adrenomedullin and related peptides

Adrenomedullin (ADM) exerts potent vasoactive effects in the microvasculature. These activities have been most extensively studied in the cutaneous microcirculation. In this review we examine the knowledge gained to date of the ability of ADM to influence microvascular effects that include increased blood flow, microvascular permeability (leading to edema formation), neutrophil accumulation and cutaneous thermal hyperalgesia. ADM is structurally related to the vasodilator neuropeptide calcitonin gene-related peptide (CGRP). The peptides are considered to act via a family of receptor activity modifying proteins (RAMPs) that interact with a G-protein linked receptor, calcitonin receptor-like receptor (CRLR). A correlation of microvascular activity with effects mediated via CRLR and RAMP is discussed.

The calcitonin gene-related peptide (CGRP) antagonist CGRP(8-37) blocks vasodilatation in inflamed rat skin: involvement of adrenomedullin in addition to CGRP

The neuropeptide calcitonin gene-related peptide (CGRP) is a potent microvascular vasodilator in rat skin and effects are antagonised by CGRP(8-37). In this study, CGRP(8-37) significantly (P<0.05) inhibited the time-dependent (3-5 h) increase in skin blood flow measured in the anaesthetised rat, after intradermal administration of the inflammatory cytokine interleukin-1beta (3 pmol/site), indicating the involvement of CGRP1 receptors. The CGRP-related peptide adrenomedullin (ADM) is also a potent vasodilator in rat skin, with effects antagonised by CGRP(8-37). We show that ADM mRNA expression is increased in rat skin after treatment with IL-1beta and that the IL-1beta-induced blood flow is blocked by a selective ADM antibody (P<0.05). Thus ADM is expressed locally in the inflamed cutaneous microvasculature where it can, in addition to, or as an alternative to CGRP, contribute to IL-1beta-induced vasoactive effects.

Comparative effect of Phoneutria nigriventer spider venom and capsaicin on the rat paw oedema

Capsaicin, the pungent component of hot peppers, and the venom of the spider Phoneutria nigriventer are able to activate sensory nerves resulting in cutaneous neurogenic plasma extravasation. This study was undertaken to compare the ability of these substances to evoke oedema in the rat hind-paw and mechanisms underlying this effect. Subplantar injection of either Phoneutria nigriventer venom (PNV; 1-100 microg/paw) or capsaicin (10-200 microg/paw) caused a significant paw oedema that was potentiated by CGRP (10 pmol/paw). In rats treated neonatally with capsaicin to deplete neuropeptides, the paw oedema induced by either PNV (100 microg/paw) or capsaicin (100 microg/paw) was partially reduced (P<0.05). The tachykinin NK1 receptor antagonist SR140333 (0.2 micromol/kg; i.v.) prevented the paw oedema induced by the tachykinin NK1 receptor agonist GR73632 (30 pmol/paw) and partially reduced paw oedema induced by PNV or capsaicin. Treatment of rats with compound 48/80 (5 mg/kg; s.c. 3 days) or with both H1 receptor antagonist (mepyramine; 1 nmol/paw) and 5-HT receptor antagonist (methysergide; 1 nmol/paw) significantly inhibited PNV- or capsaicin-induced paw oedema. The combined treatment with mepyramine and methysergide and SR140333 further reduced PNV- and capsaicin-induced paw oedema. The bradykinin B2 receptor antagonist Hoe 140 affected neither PNV- nor capsaicin-induced responses. Our results suggest that PNV and capsaicin each induce paw oedema that is partially mediated by activation of sensory fibers culminating in the release of substance P as well as by activation of mast cells which in turn release amines such as histamine and 5-HT.

Identification and structure of the nerve growth factor binding site on TrkA

Nerve growth factor (NGF) is involved in the development and maintenance of the nervous system and has been implicated as a possible therapeutic target molecule in a number of neurodegenerative diseases, especially Alzheimer's disease. NGF binds with high affinity to the extracellular region of a tyrosine kinase receptor, TrkA, which comprises three leucine-rich motifs (LRMs), flanked by two cysteine-rich clusters, followed by two immunoglobulin-like (Ig-like) domains. We have expressed the second Ig-like domain as a recombinant protein in E. coli and demonstrate that NGF binds to this domain with similar affinity to the native receptor. This domain (TrkAIg(2)) has the ability to sequester NGF in vitro, preventing NGF-induced neurite outgrowth, and in vivo, inhibiting NGF-induced plasma extravasation. We also present the three-dimensional structure of the TrkAIg(2) domain in a new crystal form, refined to 2.0 A resolution.

Neurokinin-1 receptor agonists are involved in mediating neutrophil accumulation in the inflamed, but not normal, cutaneous microvasculature: an in vivo study using neurokinin-1 receptor knockout mice

We have used tachykinin neurokinin-1 receptor (NK1 receptor) knockout mice to learn of the link between NK1 receptors and neutrophil accumulation in normal naive skin, as compared with inflamed skin. Intradermal substance P (300 pmol) induced edema formation in wild-type mice, but not in NK1 knockout mice, as expected. However, in contrast to IL-1beta (0.3 pmol), substance P did not induce neutrophil accumulation in wild-type mice. IL-1beta-induced neutrophil accumulation was similar in wild-type and knockout mice, but a significant (p < 0.05) contributory effect of added NK1 agonists, which by themselves have no effect on neutrophil accumulation in normal skin, was observed. The results support the concept that NK1 agonists such as substance P cannot act on their own to mediate neutrophil accumulation in naive skin and provide direct evidence that in inflamed skin, under certain circumstances, the NK1 receptor can play a pivotal role in modulating neutrophil accumulation during the ongoing inflammatory process. We investigated responses to two inflammatory stimuli (carrageenin and zymosan). Neutrophil accumulation was significantly attenuated (p < 0.001) in carrageenin- but not zymosan-induced inflammation in NK1 knockout mice. The carrageenin (500 microg)-induced response was inhibited (p < 0.05) by a NK1 receptor antagonist, SR140333 (480 nmol/kg i.v. at -5 min), in the wild-type group. The bradykinin B1 and B2 receptor antagonists (desArg9[Leu8]bradykinin and HOE 140) each reduced neutrophil accumulation to carrageenin in wild-type animals (p < 0.05), but did not cause further reduction of the suppressed response of knockout mice. The results provide evidence that kinin receptors participate in NK1 receptor-dependent neutrophil accumulation in inflamed mouse skin.

Generation of peroxynitrite in localised, moderate temperature burns

Simultaneous generation of nitric oxide (NO*) and superoxide (O2-) can lead to the formation of peroxynitrite (ONOO-), a potent oxidant that has been implicated in the pathogenesis of a number of disease states. This study was designed to investigate the possible generation of ONOO- in local cutaneous tissues following thermal injury. Male Wistar rats were anaesthetised in a nonrecovery procedure and subjected to a small (1 cm diameter), abdominal burn of moderate temperature (50 degrees C, 5-15 min). At either the 60 or 180 min time point postburn the animals were killed, and skin sites were removed and homogenised. An ELISA was used to quantify protein bound 3-nitrotyrosine (3NT), a biomarker for ONOO- in the rat skin. In separate experiments the accumulation of [125I]-albumin in thermally injured skin was used to calculate plasma extravasation. Thermal injury (50 degrees C, 10 min) to rat abdominal skin caused a significant increase in both 3NT (p < 0.05) and oedema formation (p < 0.001) when compared to unheated control sites at the 180 min time point postburn. This data is the first to show protein nitration in thermally injured, oedematous skin and strongly suggests that ONOO- is generated in thermally damaged cutaneous tissue.

Involvement of vanilloid receptors and purinoceptors in the Phoneutria nigriventer spider venom-induced plasma extravasation in rat skin

Phoneutria nigriventer venom causes stimulation of capsaicin-sensitive primary afferent neurons in the rat dorsal skin, leading to neurogenic plasma protein extravasation due to the release of tachykinin NK(1) receptor agonist. In this study we further investigated the mechanisms involved in the venom-induced activation of capsaicin-sensitive primary afferent neurons. The plasma extravasation in response to venom intradermally injected was measured in Wistar rats as the local accumulation of i.v. injected 125I-labelled human serum albumin into skin sites. The tachykinin NK(1) receptor agonist, D-Ala-[L-Pro(9),Me-Leu(8)]substance P-(7-11) (GR73632; 10-100 pmol/site), induced a significant plasma leakage that was abolished by the selective tachykinin NK(1) receptor antagonist, (S)-1-[2-[3-(3,4-dichlorphenyl)-1 (3-isopropoxyphenylacetyl) piperidin-3-yl] ethyl]-4-phenyl-1 azaniabicyclo [2.2.2]octane chloride (SR140333; 1 nmol/site), whereas the leakage after venom (1-10 microgram/site) was significantly inhibited (but not abolished) by SR140333. The calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP-(8-37), failed to further reduce the residual plasma extravasation induced by venom plus SR140333. The mu-opioid receptor agonist, [D-Ala(2), Me-Phe(4),Gly-ol(5)]enkephalin (DAMGO), and the local anaesthetic, lignocaine, had no effect on the venom-induced plasma extravasation. Similarly, the L-, N- and P/Q-type voltage-sensitive Ca(2+) channel blockers (verapamil, omega-conotoxin MVIIA and MVIIC, respectively) as well as the Na(+) channel blockers, tetrodotoxin and carbamazepine, had no effect on the venom-induced effect. Neither the systemic treatment nor the local injection of ruthenium red prevented the venom-induced plasma extravasation. However, the vanilloid receptor antagonist, N-[2-(4-chlorophenyl) ethyl]-1,3,4, 5-tetrahydro-7,8-dihydroxy-2H-2-benzazepine-2-carbothioamide (capsazepine; 120 micromol/kg, i.v.), reduced by 48% (P<0.05) the venom (10 microgram/site)-induced plasma extravasation. A significant inhibitory effect was also observed with the P(2) purinoceptor agonists, adenosine 5'-triphosphate (ATP; 10 and 30 nmol/site) and adenosine 5'-diphosphate (ADP; 10 nmol/site). The involvement of histamine and/or 5-hydroxytryptamine (5-HT) in the venom-induced plasma extravasation was ruled out since neither histamine and 5-HT receptor antagonists nor depletion of mast cells by compound 48/80 affected the venom response. This was further supported by the failure of venom to degranulate in vitro peritoneal mast cells. In conclusion, only vanilloid receptors and P(2) prejunctional purinoceptors had an inhibitory effect on the neurogenic plasma extravasation evoked by P. nigriventer venom in rat dorsal skin.

Formation and loss of nitrated proteins in peroxynitrite-treated rat skin in vivo

Peroxynitrite is a reactive cytotoxic species, capable of nitrating tyrosine residues to form 3-nitrotyrosine. Little is known about the formation and loss of nitrated proteins in vivo. We have measured nitrated proteins, by enzyme-linked immunosorbent assay, in rat skin after exposure to peroxynitrite. Peroxynitrite (100-200 nmol site(-1)) was injected into the skin of anesthetized rats. At the highest dose 78.6 +/- 9.5 pmol mg(-1) protein of nitrated BSA equivalents were measured at 4 h and a significant increase was observed for 24 h after administration in skin samples. The loss of nitrated proteins from skin appeared biphasic with an initial (t(1/2) = 2 h) and slower loss (t(1/2) = 22 h). A major nitrated protein was identified as albumin by Western blot analysis. The data demonstrate that a single exposure to peroxynitrite can lead to the presence of nitrated proteins in skin for at least 24 h. The sustained presence of nitrated proteins may influence the inflammatory process in skin disease.

Use of NK(1) knockout mice to analyze substance P-induced edema formation

The mechanisms involved in tachykinin-induced neurokinin-1 (NK(1)) receptor-mediated edema formation have been studied in anesthetized wild-type and NK(1) knockout mice. Intradermally injected substance P (30-300 pmol), NK(1) agonists septide (3-30 pmol) and GR-73632 (3-30 pmol), and the mast cell-degranulating agent, compound 48/80 induced dose-dependent edema in wild-type skin, measured by the accumulation of intravenously injected (125)I-labeled albumin. Septide was 3-10x more potent than substance P. The tachykinins were inactive in knockout mice, but compound 48/80 induced a significantly greater edema (P < 0.05) than that observed in paired wild-type mice. Capsaicin (which releases endogenous neuropeptides) and exogenous tachykinins induced edema formation, which was reduced by the mast cell amine histamine H(1) antagonist mepyramine (P < 0.05). These findings confirm that tachykinins mediate edema formation via the NK(1) receptor and provide direct evidence that the septide-sensitive binding site is on the NK(1) receptor. Furthermore, results suggest that edema induced by the tachykinins, although totally dependent on NK(1) receptor-mediated mechanism, contains a mast cell-dependent component. The evidence is in keeping with an NK(1) receptor on mast cells.

Lack of evidence for tachykinin NK1 receptor-mediated neutrophil accumulation in the rat cutaneous microvasculature by thermal injury

The effect of the non-peptide selective tachykinin NK1 receptor antagonist SR140333 has been investigated on oedema formation and neutrophil accumulation induced by thermal injury (50 degrees C for 5 min), mustard oil, substance P, the tachykinin NK1 agonist GR73632, and interleukin-1beta in the abdominal skin of the anaesthetised rat. SR140333 significantly inhibited (120 nmol/kg i.v.) or prevented (240 nmol/kg i.v.) the early oedema formation (0-10 min) induced by thermal injury. However, a dosing strategy which blocked NK1 receptors for 5 h (SR140333, 240 nmol/kg i.v. + 240 nmol/kg s.c.) failed to influence neutrophil accumulation measured 5 h after thermal injury. Thus, the neurogenic component mediated by NK1 receptors is important to elicit the early oedema formation, but does not influence subsequent neutrophil accumulation. Topical application of mustard oil (2%), a neurogenic inflammation stimulant, caused NK1 receptor-mediated early neurogenic plasma extravasation, but did not induce cutaneous neutrophil accumulation over 5 h. Substance P and GR73632 at high doses (1 nmol/site) also failed to elicit neutrophil accumulation. Neutrophil accumulation induced by interleukin-1beta (0.03-3 pmol i.d.) was not affected by SR140333 pretreatment. In conclusion, despite an early pronounced tachykinin NK1 receptor-dependent oedema response after thermal injury, the results suggest that subsequent neutrophil accumulation is not mediated by NK1 receptors. Furthermore, we have not obtained any evidence to suggest that either endogenous or exogenous tachykinins can directly induce neutrophil accumulation in the rat cutaneous microvasculature.

Interaction of amylin with calcitonin gene-related peptide receptors in the microvasculature of the hamster cheek pouch in vivo

1. This study used intravital microscopy to investigate the receptors stimulated by amylin which shares around 50% sequence homology with the vasodilator calcitonin gene-related peptide (CGRP) in the hamster cheek pouch microvasculature in vivo. 2. Receptor agonists dilated arterioles (diameters 20-40 microm). The -log of the concentrations (+/- s.e.mean; n = 8) causing 50% increase in arteriole diameter were: human betaCGRP (10.8 +/- 0.3), human alphaCGRP (10.8 +/- 0.4), rat alphaCGRP (10.4 +/- 0.3). Rat amylin and the CGRP2 receptor selective agonist [Cys(ACM2,7]-human alphaCGRP were 100 fold less potent (estimates were 8.5 +/- 0.4 and 8.2 +/- 0.3 respectively). 3. The GCRP1 receptor antagonist, CGRP8-37 (300 nmol kg(-1); i.v.) reversibly inhibited the increase in diameter evoked by human alphaCGRP (0.3 nM) from 178 +/- 22% to 59 +/- 12% (n = 8; P < 0.05) and by rat amylin (100 nM) from 138 +/- 23% to 68 +/- 24% (n = 6; P < 0.05). CGRP8-37 did not inhibit vasodilation evoked by substance P (10 nM; n = 4: P > 0.05). 4. The amylin receptor antagonist, amylin8-37 (300 nmol kg(-1); i.v.) did not significantly inhibit the increase in diameter evoked by human alphaCGRP (0.3 nM) which was 112 +/- 26% in the absence, and 90 +/- 29% in the presence of antagonist (n = 4; P < 0.05); nor that evoked by rat amylin (100 nM) which was 146 +/- 23% in the absence and 144 +/- 32% in the presence of antagonist (n = 4; P > 0.05). 5. The agonist profile for vasodilatation and the inhibition of this dilatation by CGRP8-37, although not the amylin8-37 indicates that amylin causes vasodilatation through interaction with CGRP1 receptors in the hamster cheek pouch.

Activation by Phoneutria nigriventer spider venom of autonomic nerve fibers in the isolated rat heart

In the isolated rat heart, Phoneutria nigriventer spider venom (10-100 microg) produced a dose-dependent and reversible rise in left ventricular developed pressure. A low dose (10 microg) of venom induced a short-lasting, positive inotropic effect (P < 0.05) with no change in heart rate or coronary flow. At a dose of 50 microg, the venom caused significant positive inotropic and chronotropic responses associated with occasional ventricular arrhythmia, whereas coronary flow was not significantly affected within 10 min after venom administration. The highest dose of venom (100 microg) caused bradycardia, transient cardiac arrest, rhythm disturbances and an increase in end diastolic pressure followed by a reduction in coronary flow. Hearts treated with the non-selective beta-adrenoceptor antagonist propranolol (3 microM) and the selective beta1-adrenoceptor antagonist CGP-20712A (10 microM) were protected against all the cardiac actions of the venom. The selective beta2-adrenoceptor antagonist butoxamine (10 microM) slightly reduced the cardiac response to 50 microg, but not to 100 microg of venom. Butoxamine also prevented the reduction in coronary flow induced by 100 microg of venom. Hearts from reserpine-treated rats (5 mg kg(-1) day(-1), i.p., for 2 days) showed a marked decrease in all venom (< or = 100 microg)-induced cardiac responses. The muscarinic receptor antagonist atropine (1 microM) slightly potentiated the response to 50 microg of venom but had little or no effect on the responses to 100 microg of venom. The cardiac responses to venom (50-100 microg) were unaltered in hearts from rats treated with 8-methyl N-vanillyl-6-nonenamide (capsaicin; 50 mg/kg, s.c.). These findings indicate that P. nigriventer venom releases norepinephrine from cardiac sympathetic nerve endings and this may explain the observed increase in contractile force and heart rate.

Activity of tachykinin NK1 and bradykinin B2 receptor antagonists, and an opioid ligand at different stimulation parameters in neurogenic inflammation in the rat

Stimulation of the saphenous nerve in the anaesthetised rat results in cutaneous neurogenic oedema formation. We have examined the effect of a tachykinin NK1 and a bradykinin B2 antagonist, and a mu-opioid agonist on plasma extravasation observed in response to two differing nerve stimulating parameters (10 V, 1 ms, 2 Hz and 25 V, 2 ms, 10 Hz). The NK1 antagonist SR140333 abolished oedema, supporting the theory that an NK1 agonist is a primary mediator of neurogenic oedema. The B2 antagonist HOE 140 had no effect, indicating a lack of involvement of B2 receptors in this response. The pre-junctionally acting mu-opioid agonist DAMGO significantly inhibited oedema formation at the 10 V, 1 ms, 2 Hz (P < 0.001), but not the 25 V, 2 ms, 10 Hz stimulation parameters. Thus a post-junctionally acting NK1 antagonist inhibited neurogenic oedema formation induced by both stimulation parameters, whilst a pre-junctionally acting mu-opioid agonist acted only at 10 V, 1 ms, 2 Hz parameters. These findings could be of interest with respect to therapeutic approaches of pathophysiological conditions which involve a neurogenic component.

Neurogenic cutaneous vasodilatation and plasma extravasation in diabetic rats: effect of insulin and nerve growth factor

1. Neurogenic vasoactive responses in rat skin were investigated following 8 weeks of streptozotocin-induced diabetes to determine the effect of diabetes and of treatment with insulin and nerve growth factor (NGF) treatment. 2. Diabetic rats were divided into three groups: untreated; insulin (4 IU day(-1) by s.c. implant weeks 4-8) treated; Nerve Growth Factor, NGF, (0.2 mg kg(-1) three times weekly, weeks 4-8) treated. A fourth group served as a non-diabetic control. 3. Electrical stimulation of the saphenous nerve (10 V, 2 Hz, 1 ms for 30 s) increased blood flow in the ipsilateral paw skin, as measured by laser Doppler flowmetry. The peak increase was similar between groups, but the time taken for flow to return to a steady baseline was significantly (P < 0.01) reduced in untreated diabetic rats, when compared with non-diabetic controls, but not significantly reduced in the insulin- or NGF-treated diabetic groups. 4. A second stimulation of the saphenous nerve (10 V, 2 Hz, 1 ms for 5 min) produced plasma extravasation, measured by the extravascular accumulation of 125I-albumin, in the skin. Plasma extravasation was significantly attenuated (P < 0.001) in the untreated diabetic group, but not the insulin-treated group, compared to non-diabetic controls. Plasma extravasation was present, though reduced, in the NGF-treated group. 5. Plasma extravasation induced by intradermal injections of substance P with and without CGRP was similar in all groups indicating no decrease in vascular responsiveness to exogenously applied neuropeptides. The results suggest that release of neuropeptides is diminished in diabetes and that treatment with either insulin or NGF can restore neurogenic microvascular vasoactive responses towards normal.

Neurogenic oedema and vasodilatation: effect of a selective neuronal NO inhibitor

The effects of a neuronal nitric oxide synthase (nNOS) inhibitor, 1-(2-trifluoromethylphenyl)imidazole (TRIM) on rat sensory saphenous nerve-induced neurogenic inflammation were investigated. TRIM (50 mg kg-1, i.p.), but not 2-trifluoromethylphenol (TRIMPOH) which lacks nNOS inhibitory activity, inhibited neurogenic oedema by 55.8 +/- 6.5% (n = 6, p < 0.05). The effect of TRIM was partially reversed by L-arginine (100 mg kg-1, i.v., p < 0.01). TRIM also caused a reduction (p < 0.05) in neurogenic vasodilatation but had no effect on neuropeptide responses induced by substance P + CGRP. Topically applied TRIM (100 microliters of 150-250 mg ml-1) inhibited neurogenic oedema (p < 0.01). Thus, use of this recently described nNOS inhibitor has provided new evidence to further the hypothesis that nNOS plays a role in modulating sensory nerve-mediated neurogenic inflammation.

Kinin B2 and B1 receptor-mediated vasoactive effects in rabbit synovium

Blood flow in response to bradykinin (BK, B2 receptor agonist) and desArg9 BK (B1 receptor agonist) was measured by laser Doppler flowmetry, as a reversal of noradrenaline (50 nmol)-induced decreased blood flow, in the synovium of the anaesthetised rabbit. Either a pretreatment (-6 h) of the cytokines IL-1beta (10 pmol) plus TNFalpha (10 pmol) or saline was injected intra-articularly. BK increased blood flow irrespective of pretreatment, whereas desArg9BK increased blood flow only in the cytokine-pretreated joints. The B2 antagonist HOE 140 reversed (p < 0.01) only the BK responses, and the B1 antagonist desArg9Leu8BK only reversed desArg9BK responses (p < 0.001). A nitric oxide synthase inhibitor, (L-NAME, 10 micromol kg(-1)), reversed the effects of the kinins (p < 0.05), but not sodium nitroprusside-stimulated responses. The results suggest that the B2 receptor is constitutively expressed and that the B1 receptor can mediate responses in inflamed tissues. The results, in addition, indicate that the responses, mediated via both receptors, are nitric oxide-dependent.

Phoneutria nigriventer spider venom induces oedema in rat skin by activation of capsaicin sensitive sensory nerves

Phoneeutria nigriventer venom induces oedema formation when injected in the rat dorsal skin and such oedema is, in part, dependent on the stimulation of tachykinin NK1 receptors. This study investigated whether Phoneutria nigriventer venom acts directly on tachykinin NK1 receptors, or indirectly to activate sensory neurones which in turn release a tachykinin NK1 receptor agonist. The plasma extravasation induced by Phoneutria nigriventer venom (1-10 microg/site) in neonatally capsaicin (8-methyl N-vanillyl-6-nonenamide)-pretreated rats was substantially attenuated (P < 0.05) but the response to either the tachykinin NK1 receptor agonist GR73632 ((deltaAva[L-Pro9, N-MeLeu10] substance P-(7-11) 30 pmol/site) or bradykinin (0.3-3 nmol/site) was not affected. These results indicate that Phoneutria nigriventer venom stimulates sensory nerves indirectly. The lack of effect of capsaicin-pretreatment on the GR73632 and bradykinin responses indicated that the tachykinin NK1 and bradykinin B2 receptors remained functional. There was no evidence to suggest that Phoneutria nigriventer venom contains a tachykinin NK1 receptor agonist.

Effect of peroxynitrite on plasma extravasation, microvascular blood flow and nociception in the rat

1. Peroxynitrite (ONOO-) is a cytotoxic species, formed by the reaction between nitric oxide and superoxide free radicals, that may be involved in inflammation. In this study we have investigated the effect of peroxynitrite on plasma extravasation and microvascular blood flow in the dorsal skin and on nociceptive responses in the hind paw of the rat. 2. Male Wistar rats were anaesthetized and their dorsal skin shaved. Plasma extravasation was measured by the extravascular accumulation of 125I-labelled albumin over 0-45 min and 0-240 min. Blood flow was measured by laser-Doppler flowmetry over 0-240 min. Studies in the hind paw were carried out in the conscious rat. Hind paw weight changes were determined by volume displacement and nociception by a mechanical hyperalgesia technique. 3. Intradermal (i.d.) peroxynitrite (100-200 nmol site-1) produced a significant (P < 0.01) dose-dependent increase in plasma extravasation in dorsal skin over 0-45 min which was not increased over 45-240 min. Plasma extravasation was significantly (P < 0.001) decreased in rats pretreated with the anti-inflammatory steroid dexamethasone (1 mg kg-1, i.v.; -180 min), but not modulated by treatment with the hydrogen peroxide deactivator catalase (2200 u site-1), or the superoxide scavenger superoxide dismutase (500 u site-1), effective doses of the tachykinin NK1 antagonist SR140333 (1 nmol site-1), the cyclo-oxygenase inhibitor indomethacin (358 mumol site-1), or combined pretreatment with mepyramine (histamine H1-receptor antagonist; 2.8 nmol site-1) and methysergide (5-HT antagonist; 1.9 nmol site-1). 4. Microvascular blood flow was significantly (P < 0.05) increased 30 and 120 min after i.d. peroxynitrite (100 nmol site-1) in dorsal skin and remained raised until the end of the recording period (240 min). The increase in blood flow was unaffected by dexamethasone (1 mg kg-1, i.v.; -180 min) or indomethacin (10 mg kg-1, s.c.; -30 min). 5. Hind paw volume was significantly (P < 0.001) increased 30 min after intraplantar peroxynitrite (87.5 and 175 nmol paw-1) and remained raised for the duration of the experiment (360 min). By comparison, nociception was not altered by intraplantar peroxynitrite. 6. These data indicate that peroxynitrite can cause an increase in both plasma extravasation and blood flow, suggesting that peroxynitrite could be of biological relevance to microvascular responses. These findings may be of importance in the pathology of inflammatory diseases in which peroxynitrite formation occurs.

A study of neurokinins and other oedema-inducing mediators and mechanisms in thermal injury

1. Mechanisms involved in the plasma extravasation observed following thermal injury of rat dorsal skin were investigated. 2. Heat applied to the dorsal skin of anaesthetized rats by a temperature-controlled skin heater (1 cm diameter) for 5 min induced temperature-dependent plasma protein extravasation at 48-48.5 degrees C, measured for up to 4 h following initiation of heat. 3. A tachykinin NK1 receptor antagonist (SR140333), a bradykinin B2 receptor antagonist (HOE 140) and a cyclo-oxygenase inhibitor (indomethacin), when given as cotreatments prior to the selected measurement period, markedly suppressed oedema formation observed over 0-1 h (P < 0.05) but not that observed over 3-4 h after injury. 4. These results indicate that although neurokinins, bradykinin and cyclo-oxygenase products may be important for the early response to thermal injury, they do not appear to play an important role in the ongoing oedema response. 5. Neutrophils accumulate at the inflammatory site by 4 h after thermal injury. Therefore, the effect of depletion of circulating neutrophils by a rat anti-neutrophil antiserum on oedema formation over the 0-4 h period was investigated. The results show that oedema formation was similar in control and anti-neutrophil-treated rats. 6. In conclusion, the data from the present study indicate that neuropeptides as well as other vasoactive mediators play a role in the acute plasma extravasation observed after thermal injury, but not in the ongoing inflammatory injury. Neutrophils, despite their presence at sites of thermal injury, do not appear to be involved in mediating the oedema formation observed up to 4 h after thermal injury.

Peroxynitrite: a mediator of increased microvascular permeability?

1. Increased expression of inducible nitric oxide synthase (iNOS) and subsequent elevation of nitric oxide (NO) levels at inflammatory sites have led to the suggestion that peroxynitrite (the reaction product of superoxide and NO) is involved in pro-inflammatory processes. The present study has investigated the ability of peroxynitrite to induce oedema formation in the rat cutaneous microvasculature. 2. Peroxynitrite was synthesized from hydrogen peroxide and acidified nitrite. Spectrophotometry was used to measure the concentration and breakdown of peroxynitrite. It was also used to determine maximum amounts of hydrogen peroxide and sodium nitrite remaining after synthesis. 3. Oedema formation in response to intradermally (i.d.) injected peroxynitrite, hydrogen peroxide and sodium nitrite was measured by the extravascular accumulation of i.v. [125I]-albumin in the anaesthetized rat. 4. Peroxynitrite (40, 100 and 200 nmol/site) acted in a dose-dependent manner to cause a mean (+/- SEM) increase in plasma extravasation of 24 +/- 2, 55 +/- 5 and 69 +/- 6 microL, respectively (n = 4), with resulting inflammatory oedema. Peroxynitrite induced significantly larger plasma extravasation than equivalent vehicle controls at doses of 100 (P > 0.05) and 200 nmol (P > 0.001). This increased extravasation appears to be a direct microvascular response to peroxynitrite administration and not due to either a raised pH, necessary to stabilize the peroxynitrite, or contaminating concentrations of hydrogen peroxide or sodium nitrite from which peroxynitrite is formed. 5. These results suggest that peroxynitrite acts to increase microvascular permeability and oedema formation. Therefore, peroxynitrite may mediate vascular pro-inflammatory effects in addition to its direct cytotoxic activity.

Sensory neuropeptides: their role in inflammation and wound healing

Vasoactive neuropeptides including substance P and calcitonin gene-related peptide (CGRP) are localised in sensory nerves which innervate blood vessels. These are the major vasoactive neuropeptides released from sensory nerve endings and both have been suggested to have roles in inflammatory and cardiovascular disease. The neuropeptides have potent effects on microvascular tone and permeability, which are seen soon after release from perivascular nerves. There is also evidence that neuropeptides can affect various activities of inflammatory cells and that sensory nerves play a role in the recovery of the healthy microcirculation during wound healing phases. This review concentrates on evidence that the neuropeptides substance P, acting via tachykinin NK1 and NK2 receptors, and CGRP, acting via CGRP1 receptors, play a pro-inflammatory role in disease and a beneficial role in wound healing. In addition, results from clinical trials of recently developed neuropeptide antagonists are discussed.